100% book a day-room at one of the city hotels. Or even near the airport. Get some rest, explore, have some good food and then head to the airport at a reasonable time, rather than wasting your entire day there.
Not only, as others have said, does the QR lounge close between flights, but spending that amount of time in any airport (lounge or not) will drive you nuts before you reach the half-way point. I once spent cluse to 14 hours in Al Safwa (did not have a choice), and that was terrible.