Well there is official and unofficial
Unofficially I have heard 30 days before is the latest to pay. That is unofficial and no verified. I would call and talk to a CM if you have doubts about being able to pay by the 45 day mark. Maybe they will work with you.
Also it is better to postpone your trip rather than cancel if you plan to go at any point in the future. Saves Money.
That is what I have found Unofficially.