It's probably a no and definitely best not to ask on InProcessing Day. Once you start Basic, the answer might (and I strongly emphasize might) depend on where you live. If you live in Colorado Springs and could leave the Academy for two hours in the evening to attend your sister's reception -- the answer might be one thing -- if it requires a plane flight home, the answer is more probably no. Evenif you live within an hour or two of the Academy, this might be a question that you can't even ask -- or resolve -- until after the first half of Basic. Maybe on Doolie Day "in" you might find someone that you could ask whether this is possible. It would require a lot of flexibility from your parents and family -- probably more flexibility than is possible while trying to put together a wedding. A true family emergency, a serious illness, a death, etc. might get a different reaction. July 4th is something of a down day with a special dinner, fireworks, etc. in the evening -- but I can't imagine you would be allowed to travel on the 2nd and re-arrive at the Academy on the 4th which would almost certainly be required if you have to fly any where to get home. I could be wrong but as a parent I doubt it. Probably too late for your sister to organize her wedding around the times that you could travel home.