It's only guessing at this point but it's been the last saturday of july for a while now and I would expect that to probably continue. However the dates/sign up usualy aren't available until around the first week of july. You could probably try to plan something around the first weekend of august and know that something will be available, just make sure you sign up online when you can.
Tips:
Not sure about your age/mobility etc. but you get to camp by parking at a nearby shopping center and packing onto busses. There is only parking at the VMAC if you have a disabled permit and you need to call in advance for those.
There is no real shade to speak of and if it happens to be a hot day it can get pretty intense. They usually sell bottled water there (concessions at the open camps are pretty good in general and fair prices, not like stadium exploit prices) but you may want to bring plenty of your own.
There is a sports authority tent there with seahawks gear and usually a 10% discount so if you plan on picking up any seahawks gear for the season that's a nice time to do it.
You'll pick up quite a bit of 'swag' if you want it so you may want to bring some kind of bag to put stuff in.
bring a blanket to sit on on the grass hill, or bring some folding chairs. Just know it's mostly a hill to view from so chairs are only gonna work in some spots.
Bring binoculars if you have them, you're really close to the field but sometimes some position groups go pretty far away.
don't forget to get a cheesy picture standing in pete carroll's parking spot like my father here.
