I used them two weeks later. That was the longest -- I do not see any reason that many months would be a problem.

They had been coated, air-dried for two hours, put in a box for about 8 hours, then froze.

If one wanted to coat a bunch for later use they could be frozen right after the initial drying -- instead of what happens if one runs out of time at the end of a printing session and risks some dark reactions to take place.