Here is a link to American Express Open card that lists a 5% discount at multiple Marriott Chains thru the end of the year.
That web page indicates "savings will be credited to your account." in the T&Cs.
I have stayed at Courtyards and paid with my OPEN AMEX and have seen the credit against the account show up in the same billing cycle. It's NOT a discount @ the hotel itself... it is applied to whichever rate you actually paid.