Venue Rental Times

The contract should be really clear. The contract should not be signed unless the hours are clear. They should also clarify in the contract the terms for setup and takedown -- unless that is primarily their responsibility. They could include an addendum and reference it from the main contract if the clarification is given to your satisfaction.

I would reach out to the venue coordinator for clarification. If it says up-to 4 hours and you have requested a start time of 6pm and they close at 9, it would make sense you only have 3 hours. But if they have arbitrarily put those times in you may need to clarify your expectations. That hour could be reserved for your set up and tear down too.