Some distros have certain crons already setup. Use:
to list them; crontab -l <username> to list them for a specific user.
If your distro has it setup already to run something, say every hour on the 47 minute mark, and you want to do something then as well; you may be able to simply make a ultra simple script, place it in the "cron.hourly" directory and that's it.
Again, I do think it's highly distro specific though...