Yeast requires a warm environment to thrive, so the room temperature will affect fermentation. If the room is chilly, you'll need to allow more time for fermenting. Alternatively, you can create a "proofing box" with your oven - simply place a cake pan or other deep dish on the bottom shelf of your oven. Place the batter on the top shelf, then close the door. This will provide a nice environment for the yeast to do its work! Make sure the oven is switched off.