I use my macbook as my main contact management system. I use iSync to sync up to my mobile, iPod Touch and other devices. I wanted to schedule the syncing to my mobile to occur every day at 2am, I found that OSX's built in cron will do this fine. I use a program called "Sync Now" to place a blue Sync button on my dock, we'll use that program to do our sync as its silent, and just works. You can grab it here.

Note: If you have anything in cron already (check with "crontab -l" then you'll need to put that in the .cron file too!).

First, open up a terminal shell and type:
nano .cron

In this file, place:
#min    hour    mday    month   wday    command
2      0     *       *       *       /usr/bin/open /Applications/Sync Now.app

Once you've done that, press CTRL+X to exit, saving changes, and then type:

crontab .cron

That will add your .cron data to the crontab and you'll be good to go from there.