25 Minutes for all series does sound challenging for a full turnaround (although if a transit operation should not be a problem).
If a turnaround critical path is prepared then Cabin Cleaning and grooming tends to be the critical element. Reduce the standard of this element to a quick 'tidy up' , then providing no catering uplift and cargo is trivial then certainly possible for the 'mythical' standard route station. However local conditions have to be taken into account (including time of day), so it appears MAN has been deemed capable of this on a regular basis.
Alternatively no analysis has been done at the individual airports and an across the board time set, which means certain stations will always 'cop' delays .