The original poster says in his profile he lives in South Africa, maybe they have different rules? He also does not state the aircraft type. For the aircraft and rules that Denti, BOAC and I are familiar with the operator would have an hour's leeway, so no obvious reason to rush the turnarounds.
As I said before there are definitely situations where unrealistic turnarounds are planned. For a one off charter if I was the customer and wanted things to run to schedule I would ask for a bit more detail on how the operator intended to avoid delays. For example there are guidelines on how long passengers need to board and of course disembark. There is obviously a difference in time required say between charter flights with lots of families and city shuttles with lots of frequent flyers.
Can the original poster give us a bit more detail, like aircraft type, number and type of passengers and some idea of why 11 hours is so important? It is potentially an interesting topic. But at the moment there is not enough data to really understand the question.