this term is based off of "pocket change" and is used similarly but in reference to time rather than money.
if someone asked you if you could afford a new lexus you might reply, "pocket change, fool." so, if someone asked if you had enough time to run to wal-mart and pick up some toilet paper you could say, "pocket time" which would be synonymous with saying, "of course."
The time it takes for a hot pocket to finish cooking in the microwave...usually 2 minutes.
Jimmy said he'd be back in pocket time, but it's already been 5 minutes.