One of my colleagues, Moshe Englerberg, told me about this wonderful Medium post by DC Palter: The uniqueness of Japanese time.
In the early days of humanity, daytime started at sunrise, midday was when the sun reached its highest level in the sky, and the day ended at sunset. The days were divided into different segments, usually based upon the activities of the group. This meant that however the day was divided, by modern standards the says were longer in what we today call summer and shorter in what we today call winter. Dividing the time between sunrise and sunset into segments was common in many areas of the world, so that by our current ways of telling time, each unit would be longer in summer than in winter. So the fact that “the length of an hour changed daily,” was a pretty universal occurrence. What is unique about the Japanese are the mechanical clocks the Japanese built to vary the periods each day as the days got longer or shorter. (Other cultures may have done the same, but this is the only one I have yet found.)
Japanese double foliot clock (Wadokei). A Japanese-made clockwatch of the 18th century, or Wadokei. Then time changed in the season because from sunrise to sunset made 12 hours and from sunset to sunrise made 12 hours.
Image from Le Musée Paul Dupuy – Horloge japonaise à double foliot (Wadokei) – Période Edo. From Wikipedia: https://en.wikipedia.org/wiki/Japanese_clock. Image licensed under the Creative Commons Attribution-Share Alike 4.0 International
Excerpt from the article
Based on the Chinese horoscope, a day was divided into 12 segments, each called an ittoki (一刻, one toki). Daytime — the time between sunrise and sunset — was divided into 6 toki. Nighttime — from sunset until dawn — was separately divided into 6 toki.
At the spring and autumnal equinox, the length of day and night is the same. But during the summer, the day is long, and in winter, the sun sets early and rises late. Consequently, the length of each toki is different between day and night. It also depends on the day of the year and on the latitude, which varys widely across Japan.
Still, without mechanized timekeeping, this ittoki system was easy to understand. People only needed to divide the day evenly. Six toki during the day meant 3 toki from dawn until noon, then 3 more toki until sunset.
Confusingly though, instead of simply counting from 0–12, toki were counted down from 9 to 4, twice each day. The numbers 1–3 couldn’t be used because they referred to Buddhist prayer times. Toki were counted down instead of up because before clocks arrived, special incense sticks were used to count down the time as it burned.
Clock makers came up with ingenious ways of adjusting the mechanical clocks for Japan’s unfixed time. Now with our smartphones, we have time accurate to the millisecond in the palm of our hands. But as I dash from one meeting to the next, desperate not to be even a minute late, I wonder what life was like when time was as simple as measuring each toki with an incense stick and listening for the temple bells.