If it's just to update the art and their sex scenes it shouldn't take that long. If he decides to do a full rework we're looking at a 6 month wait time at least.
Animated scenes are independent from the rest of the art because they consist of individual frames and not the layered images system. However, the art will have to be re-drawn because from what we already see, the models will look completely different after the re-work.
I don't find the teacher's content too bad. But I admit it does not fit together with the latest development of the game. Apart from Ms. Bisette, the animations mainly consist of a static MC and a moving girl on top of him. Even though the old system is also in place for the Roxxy story, her animations are way better.
And even though Diane/Daisy are on the new system at least in part already, it has been implemented only with the Jenny update completely.
But now, after Dogeek left the team, they are already changing it again -- the main story introduced many changes under the hood already. So I am not sure if at any point in time everything will ever be on the same level.