I would say sooner than later. If you buy today and go to ROFR within a week, you might close within 60 days if all goes well and 90+ if not (I have gone both ways already this year). If you don't make it through ROFR you start at the beginning.
In order to make a trip for August 2021 and get the accommodations you want at your home resort, 11 months out is September. If you plan to risk it and make reservations at 7 months that's a different story. Almost everyone here will recommend buying the resort you love as it is so chancy at 7 months.
If I know I am not going to use points right off that can be banked I ask for that as part of my offer. No one has refused and then you know, no matter how long ROFR or closing goes, you are covered and those valuable points will not be lost...one thing less to stress over. I consider my banked points that the seller paid dues on an offset to what I am paying per point. So I am willing to pay a bit more for loaded and much less for stripped, though I broke my own rule just last week and am in ROFR for a stripped BWV contract!
When shopping, I make a chart of resorts that I am interested in and a range of points and consider one of two use years I own. I put my target price on my chart for three types of contracts: 1. Current year points only 2. Current year and last year (freebies) 3. Current year, last year and prior year (FREEBIES - my "happy dance"). That is the holy grail to me when I see
four years worth of points on a contract (two back, current and forward). If you can not use those banked points, you figure our what you can get for renting them which offsets some of the purchase price, less the tax impact. Having the number in front of me is a good way to have my "offer" prices right there so you can act fast when you see a contract you want and make an immediate offer with confidence. I've sold two contracts, bought three and am in ROFR for one already this year, so I've been deep into the weeds for six months (actually 23 years)...bought OKW in 1996

Good luck!