Have you ever noticed that if you put cron jobs in /etc/cron.daily on a SLES machine, they seem to run at random times? I noticed it a few times, and I find it to be really annoying. Say, I rebooted a machine yesterday around 14:00, and today at 14:15, the machine starts rebuilding the man db, backing up the rpm db, cleaning /tmp, rotating logs, etc. Huh?! Looks like a bad idea to do such things when the system is currently in use by multiple people. Imagine that you put a database backup in there, and that backup locks your database...
Well, this actually is a feature. If you read /etc/sysconfig/cron, you'll find this piece of text:
# At which time cron.daily should start. Default is 15 minutes after booting
# the system. Example setting would be "14:00".
# Due to the fact that cron script runs only every 15 minutes,
# it will only run on xx:00, xx:15, xx:30, xx:45, not at the accurate time
# you set.
You might want to set that to a non-random time on your production machines, although I would not suggest to set it the same on all of them, especially not when you are running in a virtualized environment.