Sigh.
You can find out how to create cron jobs of all kinds, including jobs that issue a
reboot(8) by using Google:
http://lmgtfy.com/?q=cron+jobs+for+beginners ... then, follow up by using the fine man pages for
cron(8) and related tools that you will find under each man page's SEE ALSO section. FreeBSD's implementation of cron may differ from what you will learn by reading guides about cron for other operating systems.
But....
In your thread in the FreeBSD forum you say you are seeing kernel panics. If that is the case, please note: a
panic is not a "freeze" or a "hang" ... it is a
crash(8).
Perhaps you should seek support from FreeBSD people for your actual problem, rather than asking for step by step "how to" instructions to circumvent it.