That's definitely a good amount of time! I've been to weddings where the bride and groom had to extend (and pay) for additional hours because everyone was having such a good time. There have been times where the last groups of people would just take it to a nearby bar or to their hotel room to keep on partying lol.
I would just keep it to those times, and if you guys want to keep on partying you can decide then
Def. see how long you'd have the venue for! We looked at different venues and they all had different ending times on their contracts/packages. We really liked how ours ended at 11pm because we felt like we'd get our money's worth, especially since we'll have it from 9am-11pm for no extra charge.