Local time, but local to what locality?
The #1 bus today going downtown was crowded at midday. Couldn't get a seat. Standing and hanging on, I happened to look at some of my fellow passengers. The gentleman sitting right next to me, fifty-ish, casually dressed but not jeans, was Indian, and he was talking to two college-age young men sitting behind him. The man checked his smartphone a couple times, and then his watch. I wondered what time it was -- I was running later than expected -- so I looked at his watch, too. The time that it indicated was clearly impossible, earlier than when I left home. Hmm, I checked my own watch. Okay, that seems reasonable. Aha, now I understand. His watch is set to Bangalore time, not Eastern US time.
The last five years or so in business, I had lots of conference calls with Asian locations. To schedule meetings sanely, or attend them on time, one had to learn the time differences of some locations, or one used the crutch of the many web sites to help with the time conversions.
US time zones all differ by a number of hours. Not so around the world. The time difference to (parts of) India and Australia includes a half-hour. That's the tip-off. For example, noon here = 10:30 or 9:30 PM there, depending on daylight savings time. The tricky part was scheduling a conference call between the two sites. Meetings that were way too early for software engineers in the US were already well into the evening in India. So we lost sleep here and they worked overtime there -- which was inconvenient for everyone, so one could think it was sort of equitable. I could never keep the half-hours straight without a cheat sheet, so I did a spreadsheet with all the plausible meeting times, including shifts for daylight time, and pinned it on the wall. (Back in the old days, I had other such conference calls with Japan and Taiwan and Singapore, which are all even numbers of hours away, but I had cheat sheets for them, too.) Now I don't really care much. It was the half-hour difference that was jarring enough to get my attention.
The man and the two students got off the bus at MIT.