Opinion by
Judge Palladino,This case arises on cross appeals filed by Pittsburgh Moose Lodge No. 46 and its insurance carrier, Fire-mans Fund Insurance Co. (Employer), and Angelo Grieco, Jr. (Claimant) from an order of the Workmens Compensation Appeal Board (Board). Employer also filed a Motion to Quash Claimants Appeal to this Court. The Board affirmed a referees order, granting Employers Petition for Modification pursuant to Section 413 of the Pennsylvania Workmens Compensation Act (Act).1 For the reasons which follow, we affirm the Board and deny Employers Motion to Quash Claimants appeal.
Claimant injured his lower back on June 14, 1982 while in the course and scope of his employment as a janitor. Thereafter, Claimant and Employer entered into a Notice of Compensation Payable wherein Claimant received $120.00 per week based upon a pre-injury wage rate of $134.00 per week.
*56On November 10, 1983, Employer filed a Modification Petition, alleging that Claimant was only partially disabled and that work was available within his physical limitations. After a hearing, the referee, by order dated December 12, 1984, granted Employers Petition for Modification directing that partial disability benefits of $32.67 per week be paid to Claimant, effective February 13, 1984. The referees order was mailed to the parties , on December 18, 1984. Thereafter, both parties appealed to the Board. Employer interposed a Motion to Quash Claimants appeal as untimely, alleging that Claimant did not file his appeal within the twenty (20) day period provided by Section 423 of the Act, 77 P.S. §853. By order dated October 4, 1985, the Board affirmed the referee, concluding that there was sufficient competent evidence to support his findings of fact and that he made no errors of law. Accordingly, the Board dismissed Employer’s Motion to Quash as moot.
On appeal to this Court, Claimant asserts that the record does not contain sufficient evidence to support the findings of fact that there were jobs available to him at the time he was released by any physician to return to work. Employer, on the other hand, asserts that Claimant’s benefits should have been suspended, rather than modified, because the referee accepted the medical testimony of Employer’s doctor, finding that Claimant could perform all of the jobs approved by him. Since 5 of the 6 jobs approved by Employer’s doctor, Dr. Zimmerman, involved full-time employment paying in excess of Claimant’s Workmen’s Compensation benefits, Employer asserts that the highest paying job should have been utilized. This, Employer asserts, would require a suspension of benefits pursuánt to Section 413 of the Act. Further, Employer, in response to Claimant’s appeal, filed a Motion to Quash, asserting that Claimant failed to file a timely appeal from the referee’s decision.
*57Our scope of review in an appeal from the Workmens Compensation Appeal Board is limited to a determination of whether an error of law was committed, constitutional rights were violated or whether there is substantial evidence in the record to support the findings of fact. Gabriel v. Workmens Compensation Appeal Board (No. 1 Contracting Corp.), 102 Pa. Commonwealth Ct. 470, 518 A.2d 895 (1986).
Claimant filed a petition for review with this Court essentially raising the same issues as he propounded before the Board. Pursuant to Pa. R.A.P. 1972, Employer filed a Motion to Quash alleging that Claimant failed to timely file an appeal from the referees decision to the Board and that this failure precludes the Commonwealth Courts consideration of Claimants appeal. Employer does not allege that the appeal from the Board to this Court was untimely, nor does it complain of any other procedural irregularity.
The timeliness of Claimants appeal from the order of the referee to the Board goes to the jurisdiction of that tribunal to entertain the appeal. If the appeal was untimely, the Board did not have jurisdiction to reach the merits. See Workmen's Compensation Appeal Board v. The Budd Co., 29 Pa. Commonwealth Ct. 249, 370 A.2d 757 (1977). Thus, Employer should have raised the timeliness issue in its Petition for Review. Pa. R.A.P. 1972 states: “Subject to Rule 123 (applications for relief), any party may move: ... (7) To quash for any other reason appearing on the record.”
[Application under Pa. R.A.P. 123 is permitted only where no other form is elsewhere prescribed by the Rules of Appellate Procedure.- Pa. R.A.P 1502 provides, in pertinent part, that the petition for review, when used to appeal administrative agency actions, ‘shall be the exclusive procedure for judicial review of a determination *58of a governmental unit.’ (Emphasis added.) Clearly then, resort to an application under Pa. R.A.P. 123 is in error when it merely raises matters which either were or should have been raised in a petition for review.
Tempero v. Department of Environmental Resources, 44 Pa. Commonwealth Ct. 235, 240, 403 A.2d 226, 229 (1979). (Emphasis in original.) Since it relates to the jurisdiction of the Board rather than to any flaw in the mechanics of the appeal to this Court, there is clearly an issue which should have been raised in a Petition for Review. As such, the Motion to Quash Claimant’s appeal to this Court is dismissed.
However, we need not reach the merits of Claimant’s appeal. Claimant had twenty (20) days after notice of the referee’s order was served upon him to appeal to the Board. Section 423 of the Act, 77 P.S. §853. The twenty day limit is jurisdictional, Fritz v. Workmen's Compensation Appeal Board (Kim Manufacturing Co.), 107 Pa. Commonwealth Ct. 168, 527 A.2d 636 (1987), which issue may be raised at any time sua sponte by an appellate court. Commonwealth v. Little, 455 Pa. 163, 314 A.2d 270 (1974); Wagner v. Pennsylvania Board of Probation and Parole, 104 Pa. Commonwealth Ct. 403, 523 A.2d 155 (1987).
The decision of the referee was mailed on December 18, 1984. Notice is deemed served on the day when mailed. Riley Stoker Corp. v. Workmen's Compensation Appeal Board, 9 Pa. Commonwealth Ct. 533, 308 A.2d 205 (1973); Section 406 of the Act, 77 P.S. §717. Thus, to have been timely, Claimant must have placed his appeal in the mail on or before January 7, 1985. Claimant’s appeal is dated January 8, 1985 and is postmarked January 9, 1985. Claimant’s appeal to the Board was untimely and, thus, the Board lacked juris*59diction to consider the issues raised by Claimant. As such, it was error for the Board to dismiss the Motion to Quash as moot and address the merits. Fritz.
Lastly, Employer asserts that the referee erred by modifying rather than suspending benefits because he adopted the medical and vocational testimony of witnesses which established the availability and suitability of full-time work.2 The referee, as factfinder, resolves questions of credibility and is free to accept or reject the testimony of any witness in whole or in part. Pasquarello v. Workmen's Compensation Appeal Board (Bechtel Power Corp.), 97 Pa. Commonwealth Ct. 307, 509 A.2d 933 (1986).
*60In the Ninth Finding, the referee states that based upon Dr. Zimmermans testimony the Claimant became partially disabled from the injury and that he can perform the jobs listed in the Fifth Finding of Fact. The referee does not, however, adopt the testimony of Dr. Zimmerman in toto, does not find that Claimant can perform the jobs in the Fifth Finding on a full-time ba*61sis nor that the jobs in this finding were available as of the date the injury resolved itself into partial disability.
In the Tenth Finding, the referee specifically found a particular job performable by Claimant on a part-time basis and available as of a date certain. Although Dr. Zimmerman and the vocational witnesses testified that Claimant could perform all of these jobs and that all were available, the referee is not bound to accept everything they say merely because he accepts a portion of it. PasquareUo. The record contains substantial evidence to support the Tenth Finding.
Accordingly, we affirm.
Order
And Now, August 28, 1987, the order of the Workmens Compensation Appeal Board in the above-captioned matter is affirmed. Employers Motion to Quash Petitioners Appeal, filed in this Court, is denied.
Act of June 2, 1915, P.L. 736, as amended, 77 P.S. §772.
The referee made the following relevant findings of feet:
FOURTH: Defendants medical proof consisted of the deposition testimony of Dr. Ronald L. Zimmerman who examined the claimant on June 15, 1983. Dr. Zimmerman reported that claimant was able to walk on his heels and toes and was able to go from a standing to a squatting position in a guarded fashion. He reported that claimant had full motion of the neck with no spasms or tenderness. There were no findings in the mid-back area. The low back examination revealed no tenderness or spasm but Dr. Zimmerman noted that the claimant could only flex forward to where his fingertips came to eighteen inches from the floor. The neurological examination was essentially normal except for release at the knees. The CT scan was reviewed and it revealed a bulging of the discs but no herniation. It was the opinion of Dr. Zimmerman that claimant has status-post lumbosacral strain with residual discomfort with no significant underlying degenerative disease. It was the opinion of Dr. Zimmerman that the claimant could perform full time light work. He is capable of sitting six to eight hours a day. He can lift up to twenty pounds infrequently and is capable of using his upper extremities for pushing, pulling and five finger dexterity.
FIFTH: Dr. Zimmerman approved the following jobs which the claimant can do within his medical limitations:
(a) Security Guard, Pittsburgh Mattress Company,
*60(b) Senior Adult Training Program,
(c) Clerk/Maintenance at the Small Mall,
(d) Light delivery driver for Thrift Optical Department,
(e) Learn and Earn Program,
(f) Security Guard for Dig and Career, Inc.
SIXTH: The defendant through its vocational expert made known to the claimant the availability of each of the jobs and advised thé respective employers of claimants physical limitations.
SEVENTH: This Referee finds that the claimant defeated his opportunity to secure the available jobs by protesting to the employers that he was unable to work.
EIGHTH: Claimants medical proof consisted of the deposition testimony of Dr. Carmello A. Ranii who has treated the claimant at various times for low back injuries. Dr. Ranii diagnosed claimants condition as sacroiliac disease, bilateral; discogenic disease and osteoarthritis and bilateral strain which he felt was a result of the work injury. Dr. Ranii pursued an aggressive course of physical therapy in treating the claimant. It was his opinion that claimant is totally disabled and is unable to perform sedentary occupations.
NINTH: This Referee has carefully considered the evidence, both medical and lay, and finds in accordance with the testimony of Dr. Zimmerman that the claimant became partially disabled from the injury and can perform the jobs listed in the Fifth Finding of Fact.
TENTH: This Referee finds specifically that claimant can perform the job as a telephone solicitor for the Learn and Earn program for the disabled. The job was available to the claimant on February 13, 1984, for which he is capable of earning $85 weekly. This is based on a twenty-five hour work week at the rate of $3.40 per hour.