Hi there!
I'm using GPG-Tools (latest version of course) under OS X.
If i change a keys expiration time you can choose one of the given values, give
it in YYYY-MM-DD or (what i want to do) in consideration of UTC in this format:
yyyymmddThhmmss to set the exact time in hours minutes and seconds.
But it seems gnupg does not set correctly set the minutes and seconds. There is
always a difference between a few minutes or seconds!
Please take a look at the attachement!