I'd assume you can wait if you buy from a retailer, they give you redemption code, but if you buy direct I believe it automatically adds 1 year to your current license length.
I bought two and just set my expiry to 24 Oct 2026. I was told by Bitwig support that if V6 comes out anytime before 24 Oct 2026 I get that with no charge.
Since they version cycle seems to be about two years, I bought a third one from Thomann that will most likely cover v7 as well.