Usage may vary. If you're only looking to stay at a specific resort for specific dates and you have to plan around scheduling vacation time from work for the adults, school schedules, sports schedules, pet sitters, etc., then I'd think you'd want to book as soon as you knew your dates.
We had very flexible work schedules even before retirement. Since DH retired in February, 2018, we've traveled extensively with our timeshares doing long spring and fall trips with some shorter stays in between. I've been able to put our trips together with no problem.
This year we had 110 nights with our spring trip. It evolved along the way more than any of our other long trips. That trip started from home in Tamarac, Florida (12 miles inland from Pompano Beach) as far west as Fairfield Glade, as far east at Williamsburg, and as far north as Ohio about 15 miles from Lake Erie. It ended with a 7 night unplanned stay over the 4th of July at Ocean Walk in Daytona Beach that popped up 15 days out. Because why not and I have a DH who gives up and goes along with the ride on the crazy train. Lol
We're just finishing up our 105 night fall into winter trip. This trip started from home, Tamarac, Florida, and took us as far west as Oceanside Pier resort in southern California. Some of it wasn't even booked yet when we left home in September. We saw so, so much, way too much, desert in Texas, New Mexico, Arizona, Nevada, and California! We did however find the Sonoran Desert with its saguaro cactus interesting and picturesque.
I don't even have an idea yet for our spring trip. By our second week back at home I'll be ready, enough of this lol, to get into full planning mode. It will be interesting to see if it proves more difficult this year with the loss of so many resorts.