Elezen growth spurts are also supposed to be very sudden, so it wouldn't feasibly be a huge plot hole that time has passed and the twins haven't visibly grown.

I'm not someone that really wants the twins to grow, I don't think it does much, but if it happens I want it to be as abrupt as possible. I want it to happen off-screen, halfway through a quest that isn't even about that. REALLY confuse the cutscene-skippers.