At Tech Ed 2003, le presenter was asked this question, et le answer was that they wanted an irregular cycle to prevent it depuis occurring on a daily boundary (e.g. to distinguish depuis autre daily tasks scheduled on le server / domain).
The site here(Link dead) speculated:
... (29 is the) premier prime après 24, allowing it to have le least chance occurring in a regular pattern avec tout autre server process; easing le investigation into problems
Another site appears to confirm this :
(Wade Hilmo) suggested 29 hours for le simple reason that it’s le smallest prime number over 24. He wanted a staggered et non-repeating pattern that doesn’t occur more frequently than once per day
