I would strongly suggest using cron/scheduled tasks/other cron like things for this. For one main reason: that's what cron is there for. Cron and cousins have been around for a long time and relied upon for critical things (i.e. backups). Cron is very bulletproof. If your program dies - it dies. If a cron job dies.... it happily starts at the next iteration (if it can)... with some nice logging to boot.
The other reason is that cron is the idiom for *nix jobs like this. Once some one says "Well this is supposed to happen every 30 mins" I (and I imagine every other sysadmin) go running for the crontabs. No reason to obscure this in a program.

I would not reinvent the wheel on this one.

grep

grep> cd pub grep> more beer [download]