On Linux and Slowlaris, crontab is in /etc/crontab
Take a look at it, i would suggest using perl -i to swap out the lines that you want to change. The script will have to be run as root of course. Man crontab will give you the encoding of the time info.
Hope this helps,
-malloc UPDATE: just read Scains's two posts, i am too used to my personal system administration to know how to do things the right way i guess :) i just couldn't think of how you could interact with crontab -e via your script. But yeah, don't use roots crontab unless absolutely necessary, thanks for the catch Scain.