Welcome to FlyerTalk,
xflies!
The offer for the Performance Business card states:
Earn 60,000 points after you spend $3,000 on purchases in the first 3 months from account opening and an additional 60,000 points when you spend $15,000 in 9 months.
Seems to me that if you open an account on the last day of the promo (Sep 16), your first statement will cut off in the middle of October, so the third statement will cut off in the middle of December, as you've stated. If so, it seems to me that the first 60K SuB points (plus 3,000 points for spend) will all post in 2024, so they will not help for 2025 / 2026 CP. The second 60,000 points should post in 2025, assuming you hit the 12K additional spend requirement next year rather than in 2024.
I haven't been playing the credit card game much in recent years, though; others can correct me if I'm mistaken.