Add routine for checking possible standby (fixes #565)

We can debate about the times, as this whole thing is a bit racey.

Initially had sleep for a minute, allow up to 30 seconds drift. 

Worked like a charm on Windows, though managed to time it quite well two times in a row on Linux for it not to work.

But then having 1 minute sleep with 1 second drift can also give bad results...

Fixes #565