It's been observed that when an event has a setup time more than 20 hours long, location assignments can be dropped. This is particularly a problem when you have an event that repeats over multiple days.
Create a separate, related event for setup for events where the setup lasts more than a few hours.
For an event with a very complicated setup, you may want to prepare the location a day (or several days) in advance and be tempted to have a very long setup time to reserve the space while the setup is being completed. Since this can lead to undesired behavior, we recommend having a separate event for a very long setup.
For example, a play in the theater needs to reserve the theater for two weeks before the first performance for the set to be built. You would create one event for the performances, and a separate event for set building, reserving the location during the time that set building happens.
One of the advantages of this approach is you can have separate security settings for the two events. The general public that should have access to information about the event itself doesn't need to know about all the setup details that the facilities staff require.