I booked a prepaid rate for next month (about halfway into the month) and I have an Amex offer where I get close to 20% back (Spend $300 get $60 back) on a Marriott booking, but it expires 3/31 so to take advantage of this, the charge needs to be made before then. I booked the stay on Saturday 3/18 (for a stay in the middle of April). When do prepaid rate reservations get charged? Is it done by the property itself or by Marriott? If they don't charge until later, is there a way to get them to charge me sooner?

I'm a Bonvoy Gold tier elite if that matters