It's obvious that Aug. 5 is the date of choice, it's usually the Saturday before pre-season. Last year with the Bills coming in and some other factor that I foget (I think the Packers had to play Monday night or something like that) caused the scrimmage to be Friday night.
I think they're late this year because of the coaching changes, Training Camp schedules haven't even been posted yet.
The Packers have also been talking to the Chiefs about practicing together this year and that may also be a factor.
When tickets go on sale I believe they will limit sales to 8 tickets/person because of the problems from last year in how it sold out.