The People, pursuant to section 16-12-102, C.R.S.1973 (1978 Repl.Vol. 8),1 have filed this direct appeal from the trial court’s judgment dismissing a criminal information filed against defendant, John Taylor Moody. We affirm.
At the conclusion of the prosecution’s case-in-chief defendant moved for a judgment of acquittal, asserting that the evidence failed to establish the offense charged in the information. The prosecution then moved to amend the information, pursuant to Crim.P. 7(e).2 The trial court *368denied the prosecution’s motion and granted defendant’s motion.
I.
Defendant was charged with a violation of section 18-4-402(l)(b), C.R.S.1973 (1978 Repl.Vol. 8), which states in pertinent part:
“(1) A person commits theft of rental property if he:
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(b) Having lawfully obtained possession for temporary use of the personal property of another which is available only for hire knowingly fails to reveal the whereabouts of or to return said property to the owner thereof or his representative or to the person from whom he has received it within seventy-two hours after the time at which he agreed to return it.” (emphasis added)
The information contains the following allegations:
“Between January 4, 1982 to the 6th day of January A.D. 1982, at the ... County of Adams in the State of Colorado [defendant] having lawfully obtained possession for temporary use of semi-trailer, serial # 68463, the personal property of the victim, American Storage [Trailer] Leasing, which property was available only for hire, did feloniously, unlawfully and knowingly fail to reveal the whereabouts of and return said property to said victim and his representative and to the person from whom the defendant had agreed to return the property....”
In its opening brief the People have conceded that the information as filed informed the defendant that the dates of the offense charged were between January 4 and January 6,1982. The People’s evidence established that the contract in question was executed on January 4, 1982, and that, pursuant to its express terms, the semitrailer was to be returned by midnight on January 6, 1982. The owner of the rental agency testified that on or about January 8 defendant telephoned him from New Mexico, disclosed where he was calling from, and indicated he would not be coming directly back to Colorado. The owner also testified that defendant at some later time spoke with another employee of the agency by telephone about the vehicle. Defendant never returned the semi-trailer to the agency, although the agency regained possession of the vehicle in May of 1982.
Section 18-4-402(l)(b) proscribes only conduct which occurs after the expiration of the rental period specified in a rental agreement. Moreover, conduct by a lessee who fails to return property as agreed which occurs within seventy-two hours of such expiration date may relieve the lessee from liability. Thus, the particular time at or during which allegedly criminal conduct by a lessee occurs is an essential element of the offense defined by this statute, to be proved by the prosecution beyond a reasonable doubt. See People v. Donelson, 194 Colo. 175, 570 P.2d 542 (1977). The gist of the offense is the failure to perform certain acts within seventy-two hours of a particular date. In prosecutions commenced under section 18-4-402(l)(b), allegations of time are, therefore, substantive allegations — not, as the People contend, mere matters of form which may be altered by amendment at any time prior to the rendering of a verdict in the absence of prejudice to the defendant. Crim.P. 7(e).
Two distinct acts are prohibited by section 18-4-402(l)(b): failure to reveal the location of property and failure to return property. The information alleged that defendant committed both such acts. The owner of the leasing agency testified, however, that defendant had in fact revealed the location of the semi-trailer to the leasing company on or about January 8, 1982. Thus, the date of the alleged offense was particularly critical in this case.3 In these *369circumstances, the trial court did not abuse its discretion in denying the People’s motion to amend the information — especially as the motion was not made until after defendant had moved for judgment of acquittal.
II.
The People also contend that the trial court erred in granting defendant’s motion for judgment of acquittal. The People assert that any variance between the evidence and the allegations of the information was immaterial and of no prejudice to defendant. We have indicated that in prosecutions commenced under this statute, allegations of time are substantive allegations, not merely matters of form. The record supports the trial court’s conclusion that the evidence did not establish that an offense occurred between January 4 and January 6, 1982, as alleged. Under these circumstances, the trial court did not err in granting defendant’s motion.
The judgment is affirmed.
. Section 16-12-102 states as follows:
“The prosecution may appeal any decision of the trial court in a criminal case upon any question of law.”
. Crim.P. 7(e) states as follows:
“The court may permit an information to be amended as to form or substance at any time prior to trial; the court may permit it to be amended as to form at any time before the verdict or finding if no additional or different *368offense is charged and if substantial rights of the defendant are not prejudiced.”
. In moving to amend the information at trial, the People recognized that the information charged that the offense was committed between January 4 and 6, 1982, and that the prosecution’s evidence had established that any conduct committed by defendant which might *369have constituted a violation of section 18 — 4— 402(l)(b) occurred after January 6, 1982.