I am always bemused by the fact that we can take off from a capital city, fly several hundred miles, at a time and speed known to ATC, only to be told in the last few minutes of cruise that we need to lose several minutes or hold. As though we all magically popped up from nowhere.
Most of us are too busy muttering expletives to complain on air.
No magic about it, simply other, possibly much smaller & slower aircraft departing from aerodromes within 20 - 30mins flight time. Could make an even bigger difference if your destination doesn't have capital city priorities.
And seriously, what would your complaints be based upon, or hope to achieve?
Wouldn't these be RPT with a known schedule.
TBH, known schedules mean nothing at the destination end. It's only actual times that have any bearing.
As for feeder fix times, +/- 30secs is workable so long as all other aircraft are that accurate, and fly expected speeds (and therein lies the crux). We regularly have an international MD80 series operator that can take anywhere from 9 to 15 minutes inside 40nm. Unfortunately we have no idea if today is Capt. Slow or Capt Quick's leg until well after the sequence is determined.
If you are early, just don't be surprised if you score a few extra track miles or further speed reductions. Likewise, if you're late, you might get asked to increase above normal profile speed.