I read on the wiki that the periodic trigger wouldn't work if the computer were sleeping, not would it trigger on the next wake. However, I just tested it twice and it does run while the system is sleeping... am I missing something?
You may be able to glean some insight from this post.
Nothing in Keyboard Maestro will work if the Mac is properly sleeping.
However the Mac has various levels of “sleep”, and in some of those Keyboard Maestro may still run.
Generally, if the screen is sleeping, locked, or screen saving, you will not be able to perform UI actions either.