August 6 sounds right on the actual selection board start date.
What type of waiver are you talking about?
Waivers for physical disqualifications are looked at every day by BUMED, NOMI and OR. They are looked at in order received, and their are only a few people looking at a lot of waivers.
For other types of waivers, such as moral waivers, they are looked at by different levels of the chain of command.
Some waivers can be approved at the district level. Other, more serious waivers require region CG level approval. Most of the time, the waivers go up with the books. But, it is a good thing to get the waiver requests up the chain before the board meets. That is your OSO's job.
Hope that helps.
Good luck and Semper Fi.