If you haven't made a reservation, you might be able to score a lower rate if you time it just right. After 5 or 6 p.m., you have a shot at getting a cheaper room if the hotel still has vacancies. Some hotels do have policies that prevent them from discounting rooms, even if that means losing business. But you might be able to get a nicer room or suite for the rate of the average double room if you ask.
On the other hand, if it's 9 or 10 p.m., the hotel is much less likely to cut you a deal because the clerk knows that you don't have as many options. So, timing is everything.