The author examines the importance of the time factor in criminal law in two areas. First, in respect of the punishability of an act, and secondly, in respect of the possible influence of this circumstance on sentencing. In the first group of issues, the analysis covered problems of decriminalization and its legal effects, a change of the legal qualification of an offence into a misdemeanor, the question of the perpetrator’s accountability (non-accountability) and age, the condition of immediacy of the attempted act, the issue of perpetration and complicity, offenses based on the time factor, the question of one act-one offense principle, and the statute of limitations. The author examines the importance of the circumstance of time for their essence. On this basis the author points out that the time factor plays a significant role as part of many criminal-law constructions. He asserts that we are not always able to deal with a more precise definition of the time factor to determine the necessary minimum or maximum time lapse. He draws attention to difficulties in defining admissible time intervals that are important for individual legal constructions. The examination of the thematic group connected with the role of the time circumstance in sentencing covered the following problems: the time of perpetration of an act versus sentencing, the perpetrator’s age, limitation of recidivism, the lapse of the probationary period required with some punitive measures, time intervals and the number of offences. The author claims that even with sentencing the role of time factor is very important. The course of time or simply the time of perpetration may in some cases act against the offender or sometimes in his or her favor.