Got this today from Waterlox.

 

When I took finishing class, I was warned that waterborne finishes need 60+ degrees and need to stay above that for at least several days.

I suspect Waterlox's information would apply closely to most oil-based varnishes

 

Low Temperature
FINISHING TIPS

Are you getting ready to start a wood finishing project?
Low temperatures can affect both the application and drying processes. Here are a few tips to keep in mind when finishing in cool weather.


1. CONSISTENT TEMPERATURES
You’ll want the Waterlox and the surface you are coating to be close in temperature and at least 50°F during application and for at least 1-2 hours afterwards.


2. FOCUS ON VENTILATION
For the first 2-4 hours, you want to get the air near the project exhausted to the outside. Fans directed outward in nearby windows will bring fresh air in and force contaminated air out. It is important that you do not blast air directly onto a surface immediately after coating as that can cause it to skin over and trap some of the solvents.


3. KEEP THE AIR MOVING
After the first few hours, shift the focus to keeping the air circulating. You do not need hurricane force winds inside your room, but a box fan on a low setting blowing gently over the surface will help IMMENSELY with the cure and also help to diminish any lingering odors quickly. You can turn heaters back on (no open flames in the same room), partially close windows, etc. to help maintain a warmer environment, but remember that air flow will always be more important than warm temperatures!


4. BOX FANS ARE BEST
Forced air and ceiling fans will be nowhere near as effective as directional air flow that you can achieve with a cheap box fan. Set these fans on a low to medium setting for a gentle breeze.

2 hours ago, kmealy said:

4. BOX FANS ARE BEST
Forced air and ceiling fans will be nowhere near as effective as directional air flow that you can achieve with a cheap box fan. Set these fans on a low to medium setting for a gentle breeze.

Good idea and also good for keeping the shop cooler in summer.  I got a smaller 9 inch one but mounted it just over my head on some garage door opener T track.  Allows me to keep it out of the way when not in use, and pull it to where I do need it when the time comes.  Just throwing this out as an idea for what to do with the fan other than put on workbench.  Be creative....