I've thinned 30 or 40 minute epoxy with acetone with excellent results. No sticky or rubbery residue. If you are using alcohol use 90% or better yet use denatured alcohol. The cheap over the counter 50% stuff has a lot of water in it. I'm not sure but I think this is what can give some epoxy that rubbery feel.

BTW the can of acetone actually says it's a thinner for epoxy and foberglass finishing resins.