In some cases with the benefit of hindsight yes. If the flights are fully loaded ethnic charters with associated cleaning and you need 16 tones of fuel, with so so handling you are going to struggle with 45 minutes. On the other hand city shuttles with bus boarding, self cleaning and fuel tankering can make 25 minutes very achievable. Some operators appear to pad the block times to compensate. But there are definitely rotations that after the magic three months need to be rescheduled.