Ngannou didn't take time off. He said he wanted to fight, but stalled the fight 2 times (as per Black Beast, who said the fight was first targeted for July, then for August). If someone stalls a fight 2 times, it's possible they'll stall it 3, 4 or 5 times. It was obviously a negotiation ploy. That's the reason White created the interim belt. Because there wasn't a single time an interim belt was created so fast in the history of the UFC, especially with a healthy champ. You must be extremely naive to believe the interim belt was created, because Dana wanted the fight in August, not September.
By the way there was no contract signed for September either.