delivered the Opinion of the Court.
We granted certiorari to consider the court of appeals opinion in People v. Mamula, No. 90CA2013 (Colo.App. Sept. 12, 1991) (not selected for official publication), holding that petitioner abandoned his reduction of sentence motion pursuant to Crim.P. 35(b) as a matter of law by failing to pursue it in a timely manner. We affirm.
I
Petitioner was charged with six felonies and one misdemeanor. On August 22, 1988, he pleaded guilty to three counts of second degree burglary, and the remaining charges were dismissed. Petitioner was originally sentenced to probation for two years. Shortly thereafter, the People filed a motion to correct an illegal sentence alleging that petitioner was ineligible for probation. On December 28, 1988, the district court resentenced petitioner to ten years and one day on each count of second degree burglary, each sentence to run concurrently.
Forty-seven days after petitioner was re-sentenced he filed a motion for reduction of sentence pursuant to Crim.P. 35(b). In his motion, petitioner requested that the district court “withhold judgment as to the propriety of granting a hearing and as to the final decision on [petitioner's] motion until such time as the [petitioner has] furnished the Court with documents in support of his motion.”
On July 30, 1990, 532 days after petitioner filed his motion, he requested the court to rule on his motion. Almost three months later the district court heard petitioner’s motion, about twenty months after the motion was filed — 547 days after the expiration of the 120-day period following sentencing. At this hearing, the People contended that the district court lacked jurisdiction to consider petitioner’s motion because he had abandoned the motion by failing to seek a ruling on it within a reasonable time. However, the trial court found that the delay was reasonable, and after considering the merits suspended the balance of petitioner’s sentence. The trial court ruled:
In this particular case, under these particular circumstances, the court finds that the delay was reasonable and that the defendant at his age should be granted a chance to show that he can utilize what he has learned in prison.
The court of appeals vacated the order suspending petitioner’s sentence. People v. Mamula, No. 90CA2013 (Colo.App. Sept. 12, 1991). The court found that, although the petitioner’s desire to demonstrate his rehabilitation to the trial court may be admirable,
the fact remains that the practice followed here diverts a trial court from performing its legitimate function of reviewing a sentence to determine its fairness based upon the purposes of the sentencing code as set out in § 18 — 1— 102.5, C.R.S. (1986 Repl.Vol. 8B), and it allows the court to usurp the functions of parole and commutation, which are reposed exclusively in the executive branch.
Mamula, No. 90CA2013, slip. op. at 2. The court held that petitioner had failed to pursue his motion in a timely fashion, thus *1137abandoning the motion as a matter of law. Id. at 2-3.
II
Central to resolution of this case is whether petitioner abandoned his Crim.P. 35(b) motion by failing to exercise reasonable efforts to secure a timely ruling on his motion. Crim.P. 35(b) provides:
The court may reduce the sentence provided that a motion for reduction of sentence is filed (1) within 120 days after the sentence is imposed, or (2) within 120 days after receipt by the court of a re-mittitur issued upon affirmance of the judgment or sentence or dismissal of the appeal, or (3) within 120 days after entry of any order or judgment of the appellate court denying review or having the effect of upholding a judgment of conviction or sentence. The court may, after considering the motion and supporting documents, if any, deny the motion without a hearing. The court may reduce a sentence on its own initiative within any of the above periods of time.
Petitioner argues that because a trial court’s ruling on whether to grant or deny a motion for reduction of sentence is subject to an abuse of discretion standard, we cannot reverse or modify the trial court’s decision absent a clear abuse of that discretion. See People v. Fuller, 791 P.2d 702, 708 (Colo.1990) (only in exceptional circumstances will an appellate court substitute its judgment for that of the trial court in sentencing matters); People v. Watkins, 684 P.2d 234, 239 (Colo.1984) (trial court’s sentencing decision is not modifiable absent abuse of discretion). Petitioner contends that from this premise we must conclude that a trial court’s decision on whether or not a delay in ruling on a Crim.P. 35(b) motion is reasonable is subject to an abuse of discretion standard. While we agree that the trial court is in the best position to determine the reasonableness of a period of delay in a Crim.P. 35(b) motion, we conclude that as a matter of law the trial court erred in not finding that petitioner abandoned his motion under the facts of this case.
In People v. Fuqua, 764 P.2d 56 (Colo.1988), we rejected the argument that a trial court loses jurisdiction to rule on a motion to reconsider after 120 days have passed since the imposition of sentence. However, this jurisdiction is not interminable:
In the case of a timely filed motion for reduction, the extension of the sentencing court’s jurisdiction to rule on a motion beyond the 120-day period is not interminable. It is the responsibility of the court to rule on the motion within a reasonable time after its filing.
Id. at 61 (footnote omitted). The burden of pursuing a rule 35(b) motion is on the defendant if the court fails to rule on the motion within a reasonable time:
When the sentencing court fails to act on a timely filed motion for reduction of sentence within a reasonable period of time, it then becomes the defendant’s obligation to make reasonable efforts to secure an expeditious ruling on the motion. In the absence of any reasonable effort by the defendant to obtain an expeditious ruling, the motion for reduction should be deemed abandoned.
Id. (Emphasis added.) See id. at 58. Although a “reasonable time” and “reasonable efforts” will vary with the circumstances of each individual case, they must be construed to effectuate the purposes underlying rule 35(b). No period of time can be reasonable where its purpose is contrary to the purposes and interests served by the rule. See United States v. Taylor, 768 F.2d 114, 118 (6th Cir.1985).
While rule 35(b) gives the trial court the opportunity to reexamine the propriety of the sentence imposed, it also adheres to the constitutional principle that only the executive department may modify a legally imposed criminal sentence after the conviction upon which it is based has become final. See People v. Herrera, 183 Colo. 155, 161-62, 516 P.2d 626, 628-29 (1973); People v. Lyons, 44 Colo.App. 126, 618 P.2d 673 (1980). However, as our prior cases make clear, reexamination of the sentence before it becomes final does not intrude into this area of executive power. *1138See People v. Akins, 662 P.2d 486, 487 (Colo.1983); People v. Smith, 189 Colo. 50, 51, 536 P.2d 820, 822 (1975). See also Fuqua, 764 P.2d at 60. Thus, when construing the rule, and the date a sentence becomes final, we must be mindful to assure that the district court’s authority will not be misused as a substitute for the executive department’s power of parole and commutation. Such a purpose cannot be served by permitting the trial court to hold a timely motion for reduction of sentence in abeyance for months or years while the defendant builds a record of conduct within the department of corrections. See 8A James W. Moore, Moore's Federal Practice ¶ 35.06[1] at 35-38 (2d ed. 1992). See United States v. Krohn, 700 F.2d 1033, 1037 (5th Cir.1983). The reasonable time contemplated by rule 35(b) is only that time reasonably necessary to decide the issue presented by the motion for reduction of sentence, not “a license to wait and reevaluate the sentencing decision in the light of subsequent developments.” Diggs v. United States, 740 F.2d 239, 246-47 (3rd Cir.1984).
In reaching this conclusion, we do not suggest that a trial court may not consider events favorable or unfavorable about a defendant that occurred during the “reasonable” period subsequent to filing the motion when examining the merits of that motion — the trial judge is not “required to close his eyes to developments favorable to the movant’s request....” Taylor, 768 F.2d at 118 n. 4. See People v. Bridges, 662 P.2d 161, 164-65 (Colo.1983) (in ruling on a Crim.P. 35(b) motion the trial judge may properly consider evidence of defendant’s improved conduct while in prison). Nor is the trial court prohibited from taking a defendant’s unfavorable conduct into account when ruling on a Crim.P. 35(b) motion. See Mikkleson v. People, 199 Colo. 319, 618 P.2d 1101, 1102 (1980) (all relevant and material facts to be considered); Spann v. People, 193 Colo. 53, 56, 561 P.2d 1268, 1269 (1977) (trial court may consider all relevant and material information presented in support of motion to reduce sentence). Nevertheless, the time to build a record of conduct with the department of corrections is not what Crim.P. 35(b) contemplates as a reasonable time.
The only reason asserted by petitioner for his failure to pursue the motion was his desire to enter and complete programs at the department of corrections, and he justifies the period of delay in this case by the lack of rehabilitative programs in the correctional system. Not only did petitioner fail “to take reasonable efforts to secure an expeditious ruling on the motion,” Fuqua, at 58, he intentionally requested the court not to rule on his motion until he could present evidence of rehabilitation which did not even exist at the time his motion was filed. The reasons put forth for the delay, are, as a matter of law, insufficient under Fuqua to sustain a finding that the delay was reasonable.
Accordingly, by failing to pursue his motion for reduction of sentence, petitioner abandoned his motion as a matter of law. The judgment of the court of appeals is affirmed.
KIRSHBAUM, J., dissents.