The regular jobs are controled by anacron by default on RHEL6(Scientific Linux 6 or CentOS 6 are the same).
But anacron runs randomly in a day(at 3-22), so if you'd like to use cron and control jobs at a time, change like follows.
But Consider to change it if your server is virtualization environment. In virtual server, some virtual machines are running and
if they executes regular jobs at a time all,
the server will have many loading at a time. So it's necessary to change time on each machine by hand, or Keep anacron setting.