Copy the following into a file such as w2bldclean_check.sh in your $HOME.
chown username.username filname
chmod 700 filename
crontab -e
enter in and save: 0 2 * * * /home/<yourusername>/<scriptname>

#!/bin/bash

//Created by Ben Fisher
//2007-Oct-20
//Delete all but the five most recent directories in a path, for warlock2 builds.

//Pull directories, stat for mtime, sort numerically, and store (overwrite, not append, each time).
find /PATH/TO/BUILDS -maxdepth 1 -type d -print0 | xargs -0 -i stat -c "%y %n" {} | sort -nr > ~/.w2bldclean_check
//Number of directories total.
lines=`cat ~/.w2bldclean_check | wc -l`
//Number of directories minus 5 (from the correctly time-sorted list).
rmlines=$(($lines - 5))
//Sorted numerically in reverse, so tail by a value equal to 5 less than the total in the list, and then remove those.
cat ~/.w2bldclean_check | tail -`echo $rmlines` | cut -d ' ' -f 4 | xargs -i rm -Rf {}
//If less than 5, this does nothing.