Way back in college (20ish years ago) I had a friend that was living on the Illinois/Indiana boarder. He lived in Indiana but went to college in Illinois, so he was going to school in one time zone and working in another. To make matters worse, in those days Indiana had some counties that observed daylight savings and some that didn't. So he had to keep track of what shift he was on for work in his own county and if it was daylight savings or not, and in case he was making plans with any friends in other counties or just going to stores or appointments or anything, and what times he had to go to class in the other time zone. He says there were days he would show up places three hours late even though he only lived 20 minutes away because he didn't realize time had sprung forward and he had his watch set on the wrong state.

This was before smartphones, and I think the state has done away with that partially observing the time switch thing.

Personally, I'm a SuperCommuter and commute long distances for work, but only occasionally. So I'll live on the West Coast but my office is on the East Coast, so I think in office time. For me, 4am is 7am because that's what time it is for the rest of my team. Occasionally I'll have to set my internal clock to Guam Time or Amsterdam Time for a couple weeks at a time until a project is done, and it makes it much easier when I fly out there because my brain is already on that rhythm.