SysAdminGear

Change to the user you want to, then open the crontab editor:
# crontab -e

you can use this variables:

a = the minute after the hour that you want it done
b = the hour you want it done
c = Day of the Month
d = Month of the Year
e = Day of the week
f = 'command you want to execute'
* = ALL

Example:
10 0 * * * /usr/local/aplication
It will run the application every day at 12:10 AM.
* * * - means all day of the month, all month of the year, all day of the week

Other crontab commands:
crontab -e opens the editor
crontab -l lists the contents of the crontab
crontab -r removes the crontab