Originally Posted by
irishguy28
Given that jetlag would be the main noticeable factor for longhaul journeys, this "2 hour variance" in expected time would only be observable for travellers moving within the same timezone, or one timezone difference either way.
And given that there are only 4 "major" countries in the Southern Hemisphere that use DST (Chile, Paraguay, parts of Australia, New Zealand) I don't think this "2 hour variance" is much of an issue for North-South (or vice versa) travellers; jetlag and tiredness from travel is going to be the dominant factor.
That is beside the point - which is that for flights between e.g. Australia and the USA, to maintain the same arrival or departure time at one end (which may be necessary because of slots or curfews), the arrival or departure time at the other end has to be moved by 2 hours, or the scheduled flight time has to be lengthened or shortened by 2 hours, or a mixture. This can lead to other problems which all have to be worked out by the airline schedulers.
Since airlines don't really publish full timetables any more, and airports / ATC don't generally publicly release information about how they organise flight movements, a layperson has to compile their own timetables and study them carefully in order to gain the understanding needed to answer the OP.