: wanted to go on. My question is can a recently epoxied boat with no UV
: protection (varnish) withstand 5-6 hours in the sun for seven days?

Yes. Atleast yes for most usual epoxies. Most epoxies can take months of sunlight without problems. My old kayaks have still some glueings done with epoxy and no varnish. Over three years of outside storage and no signs of problems there.

When the epoxy starts to break down the surface turns to milky.