A C check takes weeks. The schedule does not pause.
A heavy check or a cabin refit takes an aircraft out for weeks rather than days. Leased capacity keeps the published schedule intact rather than cancelling around it and rebooking passengers you have already sold seats to.
The lead item is approval, not aircraft. In the Netherlands ILT works to an eight week decision period on a standard lease application, though a pre approved operator list allows ad hoc cover in hours. Which of the two you are in decides the plan.
