Sorry for commenting so many weeks later, but I truly agree with the thought of a “rotating animated pictographic”, or similar. Immersiveness is so important to a game, and even a bad game can become good with such a quality. Having a lot of wooden or stone panels and buttons to work with, with decorations in other materials, would really improve things.
Let us also not for a minute forget that the humans of the neolithicum lived their entire lives as close to nature as possible. They knew, felt, experienced and foresaw the passage of time entirely different from most modern humans. They may not have had certain words or abstract phenomena as we have, but they knew the difference in a thousand ways between the hours of the day, or the passage of the months or seasons. Even today, outdoorsmen grow accustomed to determining the hour just by looking out the window, at the shadows and at the position of the sun. They may not tell you it’s 10.23, but they will be able to tell you it’s around two hours till midday. A primitive-looking “clock” showing the passage of time, without numbers, and with the top of the clock being the 12.00, and the bottom 00.00, and with sides denoting sunrise or sunset, would work fine.
The Romans famously divided day into twelve hours, and night into twelve hours, with the sixth hour (sexta, siesta), being midday and midnight, and the rest varying in length. Something like that?