Crontab for users

Hi List, I have a simple shell service for my friends, and they would need some programs to be started at 2pm. As root, I know how to do that, but I would like they could use crontab by theirselves. All I got is a "permission denied" when I try to use crontab. Is it just safe to modify permission to crontab? Am I not leaving the door opened? Or this isn't the right way to do this? Praise