Do you have access to cron? It might be better to have a script run every 5 minutes (or less, or more, depending on the frequency these files come in), in which you can check the time stamp using the stat() function, compare it against the last time it was run (saved in a file somewhere), and decide what actions to take at that time.
While you could have a perl script that runs indefinitely, continually scanning the blessed dir until something new comes in, this is going to eat your CPU like there's no tomorrow.