Tim,
I used the same epoxy/hardener combo that you are using. I did a fill coat every 24 hours (approximately) with no sanding, and no washing. The beauty of the U.S. composites slow hardener is that it NEVER blushes.
This was 3 years ago, and if there was going to be a problem, it would have shown up by now (but it hasn't).

: Yesterday I laid out the fiberglass cloth and applied the first coat of
: epoxy. I am using U.S. Composite's 635 thin epoxy with the slow hardener.
: The drying time says 24 - 28 hours. My question is can I apply the second
: coat without sanding as long as I am doing it within the drying time
: stated?

: Thanks, Tim F.