It actually depends on what entertainment is each night. If its the house band, usually it's from 5 or 6 pm to 9 or 10 pm. If it's special guests, they might start around 8-10 and not end until 11-12 am.
We noticed that all the times we went, there is a small board placed on the sidewalk that says the entertainment for the night and the time they'll be performing. Also, you can google their site and see the special events calendar.