How do I schedule a reboot on Linux?

If it is one-time deal, you can use shutdown command with -r as argument. Instead of using shutdown now, you can add time as parameter (e.g. shutdown -r 12:30).

According to the man page: /sbin/shutdown [-t sec] [-arkhncfFHP] time [warning-message] found at --> http://unixhelp.ed.ac.uk/CGI/man-cgi?shutdown+8

Load of options to choose from but, to answer your question.

To reboot in 5 minutes: /sbin/shutdown -r 5 "reboot in five minutes"

To reboot at exactly 11:00 P.M.: /sbin/shutdown -r 23:00 "rebooting at 11:00 P.M."

NOTE: your message will be broadcast to all active terminals / sessions.

the at command is what you want.

at 5:00pm 
do
cd /
/full/path/to/init 6
done

at -l will list the at cmds