Approaches for managing how the passage of time is observed by a software execution environment, such as a virtual machine or a sandbox environment. A computer system maintains a set of physical time sources. A set of virtual time sources are computed based on the set of physical time sources. The virtual time sources operate independently of the set of physical time sources. For example, the virtual time sources may observe time passing faster or slower than the set of physical time sources. The set of virtual time sources are presented to the software execution environment as the set of time sources. Many benefits may be obtained such as higher utilization of allocated resources and avoidance of timeouts.