One time (UTC) makes sense. No more daylight time nonsense. No more conversions.
I read a book on Amelia Earhart awhile ago. Turns out they switched to Greenwich Mean Time after investigation of her loss. All of the time zones were different, and caused navigation problems. IIRC, she was to use radio ranging on the hour, and telegraph ranging on the half-hour. (Oh - and the switch on her plane between the two may have been confusing to her).
Turns out that an airplane was on the time from the last place it left. Howell Island (telegraph station) was on another time (but still an hour-increment difference). BUT - the navy ship they used for the radio, anchored just off of Howell Island, was on Hawaii time - which was a multiple of 1/2 hour off from the island!
Or something like that - but I know the ship and the island were at a 1/2 hour difference. Weird! (One of the theories is that while she was listening for telegraph, they were sending radio, and when she was listening for radio, they were sending telegraph).
And never able to lock in a position, she ran out of fuel while searching for Howell Island.