Change the method to timestamp for all the tasks

[aminya]

I'd like to change the method of checking for the state of a task to timestamp for all the tasks because the checksum method is slow. Is there a way to do this?

[pd93]

This should already be possible using the global method key.

version: '3'

method: timestamp

Seems that our docs don't really mention this at all though. This could definitely be improved.