For those of you considering coming over from UK so that you have the full picture......
The festival is on the Saturday. This year they had some events on the Friday night (cover bands, movies) and the museum and merch stands were open. HOWEVER the Friday night was for the people who were camping and not open to people with Saturday tickets only.
So if you are planning on coming over and want to do the whole thing including Friday night you will need to rent some camping gear or an RV and buy a camping pass in addition to the festival ticket.