Give it a good 4 days minimum. Epoxies blush and release gases for quite a while and it could interfere with the varnish drying. Outfit it and paddle it in the meantime. It's not going to melt without varnish. It also won't cloud etc. with a few paddles. I paddled unvarnished kayaks for weeks. Just don't leave them out in the sun for days.

Make sure you wet sand it or scrub it down good with soap and water before varnishing.