A part of that is where you are and a much bigger part is what your brooder is like. I can think of one guy up in the Michigan peninsula that is probably hatching now and his brooder is outside. I’m putting eggs in my incubator Tuesday if the hens keep providing eggs like they have been. My brooder is in the coop.
If you can provide an area warm enough that they can go to when they need to warm up and keep the food and water in a reasonably warm area, maybe in the 50’s, it doesn’t matter what the temperature is outside the brooder. It is what is going on inside the brooder that counts.
Some people report lower fertility of the eggs this time of year. Others don’t. I have not noticed a problem. If the rooster has finished the molt and the hens are laying, the eggs should be fertilized. I suspect the people reporting the problems are more likely to have really cold eggs. I gather them four times a day at least when I’m getting ready to incubate and don’t have that problem.