I believe that the factory just used what we call "Seam Sealer". In 40, 50 or 60 degree temperatures it takes awhile to fully dry. If it takes you less than a day to align the fender...
you'll surely be okay.
I usually thread each bolt in place before trying to align anything. Use some paint stirring sticks to establish body gaps. The 68-70 B body fender is a juggling act that often results in a compromise of different gaps to make everything line up. The
fender to cowl is not often the same as fender to door or fender to hood...
I've felt that if I ever have to repaint my car, I'd be tempted to focus on making the gaps as perfect as possible. This would involve welding beads alongside the edges of the fender near the cowl, then filing/grinding it to a perfect gap. I actually
did do this to the trunklid in 2002 when My buddy & I did the body and paint.