My dad also just happened to be in Effingham today, so I asked him to stop by. He just called and said he'd talked to a contractor working on-site who said he thought power would be turned on in a day or two, and the station would be open in a week or two. He didn't explain what the difference was, or why there would be a week or two between power on and opening. The only thing I can think of is that the power company could turn it on, but then Tesla may have to send somebody (from St Louis or Chicago?) to test it before it can be opened to the public.
The team has to do equipment validation and some testing, although I've found that generally after a day or two, things are working even though it's not officially "open" yet. You might find that you can plug in this weekend and it will work (then again, maybe not... don't bet on it )