Many monks here will typically suggest File::Find, but if this is for a unix system (and you don't need to worry about portability to non-unix), you'll be much better off using the standard "find" utility -- not only is it easier to use and better documented than File::Find, it is also significantly faster and places a lot less load on a cpu.

I believe all versions of "find" have a "-newer" option, that will list only files/directories that have been created/modified more recently than a specified time. (The bsd version seems to have the best range of flexibility I've seen for this option, but the GNU version is likely to be just as good. If you have the Solaris version, um... you should probably get the GNU version.) It should be easy to work out how to provide the right "-newer" parameter each time the cron job runs.

(GNU 'find' is available for MS-Windows as well, if you are somehow using a Windows version of "cron".)

(updated to fix spelling error)