These ludicrous recommendations have indeed been mentioned again and again. At many points, certainly in the UK and USA, there is no difference in procedures any longer between domestic and international departures, and thus a differential time allowance is a nonsense.

A corporate travel agent we (used to) have booked me from London City to Dublin on the 0700 departure, and sent through documentation saying this was an INTERNATIONAL flight and I therefore MUST check in 3 hours before departure. I asked them if they meant this for my flight and they said certainly yes. I then pointed out that the London City terminal building is not even unlocked until 0530 in the morning, and what did they propose I did outside the front door in the winter rain between 0400 and 0530, to which they had no sensible answer. Well, there isn't one.