You can adjust your clock by the movement of things on the sky.
The time a star or the Sun takes to move 15 degrees is exactly 60 minutes, or, 4 minutes per degree, EXACTLY.
It doesn't matter if right after rising in the East, at the top of the sky or right before setting in the west, the time and angle distribution is the same.
This means, the apparent movement of things in the sky is perfectly linear, and that have a simple explanation, the sky is still, our planet is what rotates in a very steady and constant speed exposing us to the universe.
You can NOT have this linearity if dealing with two parallel planes moving one against another, this is exactly what the flat earth model shows, a flat earth disc and a flat sky disc rotating overhead. When parallel, your angle of view changes constantly, along with the apparent size and time per distance.
The two images below, the left from the North pole and all the stars rotating around it CCW, the other from the South pole, all stars rotating around it in CW... that for itself kills the flat earth theory.
I wonder when some flat earth believer would contest and explain how this work in their flat world.