Hi; Sorry it took so long to get back to you on this!
The project I used the most on lately is an Multi - Piece " N " scale parking lot. I used Sproo-Gloo to fill the seams. Yes, it did shrink. Yes, when I sanded the residue away it was perfectly flat. The Cure time for the beads of stuff applied in the cracks was four days!. Yup, it has a long Application to Sandability time frame.
Thicker Sproo Gloo, Takes less time but workabaaility is also poorer as in terms of laying it down in the correct spot. Plus you don't want a raised dot! You want something that will blend in. There is a " Happy Medium" but you have to find one you're satisfied with.