Depends on the epoxy you are using. curing times vary per type and manufacturer. I used MAS slow cure, and the manufacturer recommended a wait of about 7 days. Curing time also varies with temperature.
This should not stop you from paddling. I did that even between varnish coats...it ends up being a little more work with the recurring cleanup, but who can stand to have a (new) kayak sitting around without using it?

Angela

: Is it esential to wait for epoxy to fully cure before applying varnish? I
: glassed in March and applied another coat of epoxy to the deck/hull seam
: last week.

: G. Hughes