If you are flying with an airline that provides a 4 sector day (or more) for any given hull, you can realistically expect a 'knock-on' delay by the time the aircraft starts its penultimate sector. It could be due to many things,
+1
Airlines want tighter and tighter turns, both for reasons of aircraft utilisation and crew utilisation. A whole day’s trip, of say 4 sectors is predicated on minimum time on the ground (anything other than that is seen as being inefficient)...it is also not uncommon in some outfits to plan crew right up to the limits of maximum flight duty periods...there is no “fat” in the system.
Now in reality once the day start you get hit by slots, baggage offload, slow push backs, and almost right from the start of sector one the timings of the final sector of the day are a work of fiction...if it gets really bad you can be looking at replacing crew on the final sector because of duty limitations, and that in itself can build in a further delay.
The answer is to build in more fat (extra aircraft extra crew) ..but that costs....