I don't know how he gets it...(This is my idea, it is not guaranteed or confirmed)
But I think you already have a plan for at least a half or a full arc.
Then he tells his editor and they both draw until they get to that part, following a plan.
He may draw at 9:00 am on Monday, then continue at 3:00 pm and finally do more at 7:50 pm.
Tuesday is still drawn and so on until it reaches the end of the week, then they publish previously drawn and fully revised chapters by Shonen Jump.
(With this batch of chapters, he leaves them saved and continues in advance).
Practically, "weekly chapters... with DELAY"