The system is actually FreeBSD but I did a system-wide find for 'at' - not available on it.

Hmm that's odd, at is a standard *nix command (try which at, should be in /usr/bin). In any case, you wouldn't really want an at job for this anyway. An at job is useful for when you want to run a command once at some point in the future. It sounds like you want to run your driver program at regular intervals. That's what a cron job is for.

man at
man cron
man crontab
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