Suppose a habitable planet is perpetually enshrouded with clouds but still has enough light seeping through to make lit and unlit portions of a day, and has an intelligent tool-making species living on it. Assume primitive civilization of some sort starts to develop. When would they start to need clocks, and how would they satisfy this need?
Keep in mind that the first "clocks" on Earth are likely over 5500 years old, and probably older. A simple vertical stick in the ground would have sufficed, but sticks of course rot. However, those first clocks on Earth were made in regions where the sky was not cloudy all day.
This question asks about the first clocks on a world where the sky is cloudy all day, everywhere, and remains cloudy all day (and all night) throughout the year.
Note: I am not asking about timing how long it takes to cook an egg. I'm asking about scheduling a meeting thirty days from now at 2:00 in the afternoon, or since it's a primitive society, scheduling a meeting thirty days from now sometime in the afternoon. Water clocks were notoriously imprecise, as were hourglasses.