Using repeater fields for a set of future dates that self-expire

Hi all,

I have a custom post type for a training course that I would like to be able to have a few dates, a lot of dates, or no dates if needs be.

I think this plugin and the repeater fields add on is exactly what I've been looking for to build this functionality.

What I'd like to know before I purchase the add on, is how I would be able to set these dates to self expire? i.e. as soon as any of the dates are in the past (or today) the custom field entry just self destructs.

Would I have to have some run daily in a cron type setup, or could I use a function that hooks in somewhere? I'm quite inexperienced when it comes to actions and filters.

Many thanks in advance,

Laurie