Hi Dave,
I have use it in cold weather, but I've never had the Epifanes take that long to dry, unless it was over uncured epoxy.
Are you vanishing bare wood and or previously vanished wood. And is it the Woodfinish Gloss or the old fashion Gloss?
Woodfinish applied too thick can take for ever to harden.
I always use either the brush thinner or spray thinner when I use either varnish and it will usually be tack free after 10 to 12 hours.
Good luck,
Paul