My measure of jet lag and time zones is “Do I get more time in bed in the morning before I have to get up?”.
But I’ve just realised that this is not a very good way to think about it, in fact it gets very confusing – and here’s why:
Let’s take the example of Spain, which is an hour ahead of UK time. More time in bed, or less?
When you first arrive in Spain you are a UK person looking at Spain, so when your alarm clock goes off at 7am (Spanish time, for your Spanish day of work) it’s really 6am UK time, where your body clock still is. So you get LESS time in bed in the morning.
However, after a few days you’re on Spanish time, and now, when you have Zoom meetings with people back in the UK, you are now “a Spanish person looking at the UK”. When those English people want a meeting at 9am their time, it’s 10am your time. Great! You can have an extra hour in bed! MORE time in bed in the morning.
And of course it’s the same in the evening – initially you’re eating a bit earlier for your body clock, and being able to stay up late because Spanish midnight is still only 11pm on your UK body clock. But once you’ve acclimatised, within a few days, you’re eating at a later hour than your UK counterparts are, so their 5pm meeting is already 6pm for you, and a late night zoom call of say 10pm UK time is 11pm your time – they are keeping you up late!