On our 2010 trip and our 2011 trip, we got our packet the exact same amount of days out each time. In our case, it was 30 days prior to arrival that we received it. On each trip, our arrival date was a Monday, and each time, we received our packet on the saturday 4 weeks out. Of course, how fast the mail travels will depend on where you live, and we live in Illinois.
As far as an alternate address, are you moving within the same town, or are you moving out of town? Just wondering if it is possible to get a PO box at the Post Office if you are concerned about it coming after you move. Or is it possible to establish a PO Box at the new Post Office? Would it even be worth it to get a PO Box just for a one time mailing?