This example randomizes the time of cron.daily execution with a stable result. Cron.daily is run at a consistent, randomized time between midnight and 7am.:
#import random
#silent random.seed($self.metadata.hostname)
# /etc/crontab: system-wide crontab
# Unlike any other crontab you don't have to run the `crontab`
# command to install the new version when you edit this file.
# This file also has a username field, that none of the other crontabs do.
SHELL=/bin/sh
PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin://bin
# m h dom mon dow user command
17 * * * * root run-parts --report /etc/cron.hourly
$random.randrange(0,59) $random.randrange(0,6) * * * root test -x /usr/sbin/anacron || run-parts --report /etc/cron.daily
47 6 * * 7 root test -x /usr/sbin/anacron || run-parts --report /etc/cron.weekly
52 6 1 * * root test -x /usr/sbin/anacron || run-parts --report /etc/cron.monthly.