The cure should be only slowed down not prevented if it is moved to a colder area. I would be sure to store it in such a way that nothing touches the new varnish since the solvents will take longer to flash off in the cold. That implies that the varnish will still be a little soft and that objects contacting it for long periods during the cold might, just might, leave marks.

Leaving my freshly varnished Lightning 17 my cold unheated garage didn't affect the finish any, I'm sure you're will be ok.

Robert N Pruden