Marriott used to only require a single stay (i.e. the award nights didn't have to be consecutive within that stay.) But it has been a few years since I last needed to do that.

I used to make use of this feature now and again back when when we stayed for longer vacations. If I needed to pay cash for a night or two of a stay with the rest of the nights being award nights, I'd always check to find the cheapest nights during the stay (usually the weekend nights). I'd then use the award cert for the pre-weekend nights and the post weekend nights. And pay cash for the those cheaper weekend nights. It would tend to save me some money. To make this work, I'd have to call the Plat line and get them to make the reservation for me, but I never had any issues doing it.

As I mentioned though, I haven't used this feature in a few years, so it may be possible Marriott changed the rules on me somewhere along the way.