You dont have to be in a hurry, as long as you set the rivets within the same day you are good. the 2 hours (or whatever the cure time is) is just how long it takes before you cant really work with it any more. Its still nowhere near dry.
What seemed to work well for me is use masking tape to mark off the area where you want pro seal on the tank (makes clean up alot easier), put pro seal on both the tank and rib, cleco every hole, then when you remove a cleco to put a rivet in, use a tooth pick to apply a little pro seal in the dimple that way the rivet is sealed too.
Once that is done, come back later and put pro seal on top on the shop end on the rivet to ensure it is all sealed up.
Its not that bad. I found my limit to be about 2 or 3 ribs at a time.