Dilema - when to paint shed?

Hi, firstly apologies if this is the wrong place to post, I couldn't find a wildlife gardening section!

OK, I attached bird boxes to my allotment shed a month or two ago, there appears to be activity and moss has been taken inside 3 of them tho no actual nesting yet - I want to encourage nesting. I think it's only blue tits so far.

I also want to paint my shed, I acquired it with my plot last year and it's needing some tlc to make sure it's serviceable for a while yet.  I have re-roofed it, tho that might need some stronger fasteners. I was waiting for the wood to dry out from winter before painting.

So, how long will I have to wait before the birds are finished nesting (if they do), I think I read somewhere that birds often have more than one brood in a season.

Any experienced blue tit wardens on here!?

Our bluetits fledge around the end of May. However, its obvious when they're gone. Just sit and listen for a few minutes.

Best time to paint any outdoor wood is when you've had a good dry spell so the wood can blot it up really well.