That's kind of a crap shoot on a sort-of holiday weekend like the one coming up.
Normally, arriving at the bridge in the late afternoon (around 3-4 p.m.) on a summer Saturday isn't usually too bad. Maybe a mile or two backup, which isn't all that horrible to deal with.
This coming Saturday, who knows? Could be okay in the mid-to late afternoon, or it could be a mess.There's really no way to predict with any accuracy.
I'm a big proponent of the "earlier is better" travel plan, as I said above. Most folks hate the idea of beginning their vacay by getting up, in the car, and on the road by 5 a.m. Thus, traffic at the bridges coming on Cape is usually pretty light during the early morning hours, and doesn't start to get slowed/ backed up until around 8 a.m.
There's plenty to see and do here while you await check-in time. Grab some grub, hit the beach, take in a museum, go window shopping, etc. Whatever you're doing ...
It's always better to be on this side of the bridge than the other, IMHO!