It seems that money is typically paid by the conference at the end of the year — so if that is how the Big 12 is doing it, we won't see the full share until the end of the 2025-26 school year. As such, still probably 18 months before BYU sees the full share.
On the flip side, BYU will hopefully see a "bonus" from our share of the CFP money, if we can keep winning through the conference championship game.