This question already has an answer here:
Early civilizations have noticed the passage of time through heavenly bodies periodically crossing the sky. With this information, they adapted according to the seasons- especially in agriculture.
This is quite confusing in my tidally-locked world (which- for convenience- is able to support life). The night-side could measure the year by observing the stars, the twilight-side experiences the sun dipping and rising on the horizon in varying degrees plus they have the growth of vegetation as reference.
Then comes the day-side that live at the edges of the sub-solar "eye". I decided their culture would be close to primitive but not savage. Living in perpetual daylight, how would they perceive time? Would they even have such concept? I suppose they can have the availability of specific trade items from the twilight-side as reference. (There's also the issue of the circadian clock, but that's a topic for another time. Let's just assume these people have 'adapted' to their environment.)