The Clock Frequency of our Universe Posted by ColinWright on Saturday August 20, 2011 @03:30AM from the jacquesmattheij.com dept. http://www.jacquesmattheij.com/The+Clock+Frequency+of+our+Universe ( 3 comments | 12 points | on HN )
http://en.wikipedia.org/wiki/Planck_time
I'm pretty sure there are others, it's quite a common trope.
In the (hopefully) real world, there was something fairly recently about possible violations of the Planck length: http://www.sciencedaily.com/releases/2011/06/110630111540.ht... (news wrapper around http://arxiv.org/abs/1106.1068 )
[1] http://www.amazon.com/Permutation-City-Greg-Egan/dp/00610548...