Normally 2 hours before arrive at the airport. Say 1 hour flight, then at least 2 hour layover. 5 hours total. Or arrive at train station 10 minutes before train. 2.5 hours on train or trains, arrive 2 hours before the flight. 4 hrs 40 minutes. Quicker or at least not longer. So where’s the problem?
That's fine until some jobsworth decides to introduce the current airport checks to the rail network. Surprised it hasn't happened yet tbh.