A poultry science professor that has bred award-winning chickens and teaches poultry disease at the University said roost mites kill more broody hens than anything else. Those may or may not be roost mites but I’d certainly treat them now.
I specifically asked him about withdrawal times for eating the eggs if you treated hens with Sevin and dusted their nests with Sevin. He said none. The eggs are perfectly safe to eat immediately. I know that’s not your question but maybe it adds to the conversation. I did not ask about any other treatment.
I’ve seen you on the forum enough to think you’ve probably seen some people ranting and raving against Sevin. You may be one of them, I don’t know. If it were me I’d treat all my chickens, not just the broody and her nest, with Sevin. If it is roost mites I’d also treat the entire coop and change out the bedding in the coop as well as in the nests.
There are other effective products out there, often containing Permethrin as the active ingredient. That can work too. But I would treat now. In my opinion the risk from the mites is much greater than the risk from the treatment.
You can treat them as you wish with whatever you wish. They are your chickens. Personally I’d use something I have confidence in.