The idea is to be able to set up a product that can be free now (but collect the card info) or, for example, 1 USD, and charge the rest later, after the event date or a set number of days later. "If you like it you pay, if not cancel and won't be charged" Like the invisible funnel.
So, on a specific date, charge the rest as a one-time fee (for the event) or as a subscription.