If you have a look through this thread it will describe all the offers...
2500 points per stay
5000 points every other stay
15000 points on x nights
20,000 points on Y nights
etc, etc...
Note some concentrate on STAYS, others NIGHTS.
Choose the one you prefer and ring the Plat line, they'll change the promo manually for you. The last time I did this the assistant just said she'd note my request and at the end of the Promo honour the points for the best offer on the nights I'd managed, which was done last week, good on yer Marriott ^