Unless the boards that need replacing interfere with your workout, I’d hold off until Spring. I don’t know where you live, but I randomly checked the temps in Greensboro for the coming week. There will be some overnight lows in the 30s. I’d prefer to have the paint/stain cure when the temps are above 50. I have no basis in science for that, just a gut reaction.

Firstly....please don't pressure wash wood. It raises the grain and leaves a fluffy texture to the deck wood. Use low grit paper on a belt sander to refresh the wood & remove the old stain. If the wood is stuck full of green moss or mold....then pressure wash before sanding. In the Winter there are more people needing work. If you want to hire it done, you could...people would be available. As long as you have 4-6 hours of over 50F weather, I'm ok with staining or painting.

If you have the time...you have your health....never know how long that will last....do it now...

I’m guessing you will probably use Pressured Treated wood for the deck. Keep in mind that it has to cure/dry before painting or staining. Our deck boards needed 4 months before we could stain it.

I’d probably repair asap, paint in the Spring. Definitely repair right away if there is any risk of someone getting injured.

I was going to recommend just waiting, but Nicole makes a compelling case for doing it now.

You might even negotiate a better price this time of year rather than in the spring when everyone wants work done.

One word of caution: I thought I needed to repair our deck which turned into needing to replace it which turned into making it a screened porch. Hahahaha. Project creep.