In OTL, longitudinal time zones (each ideally 15° wide, ±7½° around each of 24 main meridians) were introduced in the late 19th century when time tables for trains, for instance, began to require more precision and standardization across wider areas than a sundial could provide. The day had been divided into 24 equal hours long before that. This approximates solar noon at 12:00 except when daylight saving time is in effect or where timezones are shifted for political reasons.
In an ATL, how would it affect time-keeping and society as a whole if they also had 24 latitudinal time zones (each 7½° high, between two parallels) and their offsets would change regularly – e.g. 4 to 12 times a year in the US and most of Europe – to approximate sunrise at 00:00?
Assume that sunrise had always been considered the start of the day in the globally dominant culture, so it was absolutely reasonable to start the daily clock counter there.
While the equator and poles are natural extrema, the Greenwich meridian was arbitrarily selected. For the sake of familiarity and simplicity, let’s assume the 0° line in this ATL is equivalent to ours. Let the area bordered by i×7½° parallels, to the north and south, and by j×m±7½° longitudes, to the west and east, be known as a time segment.
London and Paris (hence England and France) would reside in the same time segment, but Scotland should be in the one to the north, Spain to the south of it.
In London, the earliest sunset is at 04:43 in June (03:43 without DST) and the latest at 08:06 in January and December currently. In New York City it’s between 05:24 (04:24 w/o DST) and 07:20 local time, i.e. 09:24 to 12:20 UTC. In Los Angeles it’s 05:41(–1) to 06:59, i.e. 12:41 to 14:59 UTC. (In Quito, Ecuador, the sun always rises between 05:54 and 06:17 and sets almost exactly 12 hours later every day, by the way. In Reykjavik, Iceland, it varies from 02:56 to 11:23 UTC.)
London would probably use the offsets –2, –1, ±0, +1 and +2 (i.e. 8 switches) throughout the year, where ±0 is about 6 hours ahead of OTL UTC. For NYC, it’s +3 or +4 through +6 (4 or 6 switches); LA +7 through +9 (4 switches). (In Quito the offset is always +5, whereas 16 Reykjavik needed 16 switches to cycle from –3 through +5 and back.)
I also asked a somewhat similar question where hours are not a constant length.