My guess is late Feb training then full handover in late March or April. Softs in late May. This is one of my famous "pulling it out of nowhere" speculation points.
If by handover you mean operations, I can see them being squeaked in, but I assure you it won't be full. You are correct though that they want guarantees this thing is running beautifully with no hints of issues. This is pretty close to being a similar budget to the Gringotts attraction and they want bells and whistles this time, not disappointing fart sounds.