faketime

Fake the system time for a command. More information: https://manned.org/faketime.

Fake the time to this evening, before printing the result of date:

faketime '{{today 23:30}}' {{date}}

Open a new Bash shell, which uses yesterday as the current date:

faketime '{{yesterday}}' {{bash}}

Simulate how a program would act next Friday night:

faketime '{{next Friday 1 am}}' {{path/to/program}}