Every time I need to put something in cron, I forget the format or layout of each job. I stripped this decent explanation from this site:
The format of the crontab file is as follows:
Minute (0-59) Hour (0-23) Day of Month (1-31) Month (1-12 or Jan-Dec) Day of Week (0-6 or Sun-Sat) Command
0 2 12 * 0,6 /usr/bin/find
This line executes the "find" command at 2AM on the 12th of every month that a Sunday or Saturday falls on.