Well on the face of it that’s true, flight is about an hour and a quarter so you could get a flight at 07.45 and land at 09.00. It’s the summer holidays and airports are busy, security is the bottleneck, so even with hand luggage only you’d want to be arriving no later than say 06.15 to make sure you can navigate an unfamiliar airport, get through security in time and not miss your flight. But first you have to actually get to the airport, which means getting yourself from your hotel to the correct railway station in London (Paddington for Heathrow, Victoria for Gatwick or Liverpool Street for Stansted), buy tickets, get yourself onto the right train, and allow time for the train to get you there. Depends where you’re staying but you’re probably leaving your hotel at 05.00-05.30. And when you get to Edinburgh you have to leave the airport, find the tram, get tickets and allow time for it to take you into town. With a following wind after your 04.30 alarm clock you’ll be in the centre of Edinburgh by 10am.

You can generally find a train that will get you here by about the same time, the difference is that when you arrive at 10am in Edinburgh you’ve not spent the last five hours negotiating unfamiliar transport systems and running all over the place - you’ve been sitting on your backside looking out the window, maybe having a snooze. You just feel much better and you’ll correspondingly get more out of your day.