If I remember correctly, you will usually see your points back into your account within the day you return your award. Its pretty quick.

With that said, Marriott does allow you to make award reservations without actually having to order the needed award. But I think you will have to call MR and get them to make the reservation if you don't want the points taken out of your account.

Note that if you don't call and pull the points from your account by a week before your account Marriott's system will automatically try to pull the points and order the appropriate award for you.