My only association with ground resonance testing (which is I suspect what you are interested in) has been as somebody who was waiting for the job to be finished and the results analysed, so that I could then go and do the airborne follow on stuff – or flutter testing as it then becomes.
So while I cannot really answer your question, I would say that I do not see why anybody should not be passing through the hangar as long as they stay clear of the aircraft under test – which is likely to be on jacks anyway.
As to how long the ground test would take I suppose rather depends on how much of the aircraft is being investigated (the whole structure or just a recently modified component) and also which particular vibration modes are being investigated.
Depending on the scope of the investigation I would suggest that to set it up and do it could involve anything from a day to perhaps a week or more. But you really need a reply from a guy whose day job is such testing.