Some start days, weeks, or months, some years, some never. It depends on the carrierthe state, and the fire.
If you are referring to a moratorium, I believe those are lifted when the fire is either under control or out.
My state, and perhaps all states, have a state-funded plan that will basically write a policy no matter what. I don't know if they will write a policy while a fire is burning, though.
As soon as the risk subsides. East coast issues moratoriums on Hurricanes many times in late Summer and early fall, as well as winter storms. Once the storm has passed or changed directions the moratorium is lifted