What would you want the program to do besides waiting for the appointed time? If the answer is nothing, I'd recommend you just use cron and keep it simple. As mentioned above, you don't have to worry about checking that your system is functional, whether it is your eyes on a window periodically, or some other program that pings your system, and *that* would probably run from cron.

But you could also use cron to run a perl program every minute or so which just checks a few things and decides whether it really wants to trigger your main program. That way you could do most of your scheduling in Perl.

You should also remember that if you restart your computer, you will want to have a boot script to start your uncronned program every time you restart as well.