I can’t see it being a good idea to wait if it’s something that you really want done. I would have thought it would be better to have a builder onboard & get a slot booked in.
If you are only at the thinking about it stage, it will take a while before all the plans etc. are ready anyway.
We had some work done recently on our house to remove a large brick-built cupboard in our kitchen, which also meant taking out the chimney above it.
The builder I contacted was pretty full with 3 extensions planned already for the year. Luckily, due to a delay in the planning permission for one of the projects, a window opened of a week where he could slot our job in – otherwise we’d have been waiting until October!