Also depends on the terms of the 5 day reservation's rate. So for example if you booked a rate that had a minimum 5 day stay by checking out early you will be shifted onto the hotel's rack rate.

Easiest way is to call Marriott or the hotel directly and let them tell you - and get it in writing if it means you are going to cancel as a result to reduce the chance of any hassle if you do an early check-out as a result.