Finally a solution!
Not sure what the joke here is. They are not saying that you can't go other times, they are just saying that feel free to send your teenage daughter there during those times and don't worry about her not being supervised. Personally, I don't think I would let my 9th or 10th grade kids go to these type of places sat night without adult supervision. Knowing there is school faculty supervising them would be enough for me to let then go by themselves.
Again, if they were making it assur to go other times, then I could maybe understand the cynicism (although not necessarily agree) but here they are just offering an additional 'service' which will allow my teenage to go out without me when I would want some adult supervision. I would actually commend the school for offering a solution to a problem instead of just making rules denying things to their students like many (if not most) schools do.