Many time zones: You get to a new place and look up what time zone you're in.
Well, sorta
but it's no effort at all because my timekeeping device (phone) does this automatically.
For me, the time of day is internalized in a way that I think is hard to switch. Same as how I was raised with imperial units
even though I prefer (and use professionally) metric, the intuition can be a little harder to get. But to each their own of course :)
Diesel engine, Fischer-Tropsch, Homeopathy.