I have a garage darkroom which at this time of year is about 12 degrees C. I have been heating the developer in a water bath, but there's no room for the stop and fixer. Do I need to fix for longer than I would at 20 degrees?
Probably. But run a test. Take a piece of undeveloped film and see how long it takes to clear the film. Double the length of time. This should give you how long to fix to clear your film. (or paper if you use the same dilution.)
Really though, photochemistry was developed to work best at 20C or warmer. It gets to 45F in my darkroom in the winter and I need to heat it. Regardless, I test my process about once a year.