Yesterday I had a little panic as I thought my binary watch was broken. It is just a cheap and ugly thing but I do enjoy it nonetheless.
Anyway, for the curious I typed up some of the tricks I use to read it fast.
Web
https://ruario.vivaldi.net/2023/11/06/converting-binary-to-decimal-quickly/
Gemini
gemini://ruario.flounder.online/gemlog/2023-11-06_Binary_reading_tricks.gmi
Gopher
gopher://sdf.org/0/users/r0/phlog/2023-11-06_Binary_reading_tricks.txt
Did you know you can also glance at a binary watch to approximate the time when you do not need precision?
Oh and another thing.
In the real world you will not see these two LEDs in isolation. You will still have a vague awareness of the others, even if you do not attempt to properly calculate them. More lights (particularly those close to the two right-most LEDs) will give you a rough feeling for how close you are to the crossover times.