The use of cron on OS X is discouraged. launchd
is used instead. Try man launchctl
to get started. You have to create special XML files that define your jobs and put them in a special place with certain permissions.
You'll usually just need to figure out launchctl load
http://nb.nathanamy.org/2012/07/schedule-jobs-using-launchd/
Edit
If you really do want to use cron on OS X, check out this answer: https://superuser.com/a/243944/2449