How to stop cron from running all daily tasks on startup

I noticed my computer is slow on startup sometimes, and using iotop it looks like cron's daily tasks (updatedb.mlocate in this case) run immediately on startup. If my conjecture is right, then I need to get cron to do its tasks at a more convenient time, or at least control its IO so that the rest of the system can run smoothly. Is there a way to do this?