Feature request: add option to run at least every time period

Is your feature request related to a problem? Please describe.

I want to use watchexec to view the output of a command that depends both on the contents of files I can watch and also time. As far as I know I can only trigger a re-run by touching a file or restarting watchexec.

Describe the solution you'd like

I'd like to have an option to say something like watchexec --atleast-every 30. That would cause watchexec to start a time after each time it runs, and if the timer expires it would re-run the command.

Describe alternatives you've considered I thought about running watchexec wrapped up in the classic watch command.