It doesn’t expire in 2025, it begins.
There’s a very lengthy transition language as we move to the 8 quarter measurement period. The first whole-8 quarters ends Q425. That is when the theater block hour floor is first compared and then measures every quarter thereafter. Between now and Q425, read page 10+11 of NN. Long explanation of what happens in the in between. (1.X.3+4)

[To me the theater floors are nice, but the 80% of 2018/2019 is low.]

Unrelated, anyone else notice the extra flying that wasn’t previously covered? The partner codeshare with more than 30% delta pax or 120 seats. Old language capped codeshare (language hasn’t gone away), the new language additionally COUNTS those codeshare flights now for scope ratio, in addition to those with 20% ownership, in addition to JV flights.