Change performance Default Sale End Time?

When setting up a performance, the Sale End Date defaults to the performance date and time. For most of our performances, we actually want the end time to be after the performance has started, in case some last minute patrons want to make a purchase for the event. Is there a way to change the Tessitura logic so the Sale End Time defaults to 1/2 hour past the performance end time, rather than having to adjust it for every performance build?