Does anyone else calculate their screen time limit?

lab tech here, mostly on a computer. been trying to figure out the formula: on a good day, how many hours of screen time before prodrome? usually hour 5 or 6 if nothing else is going. but it’s never just hours.

there’s sleep the night before, where i am in my cycle, whether photophobia from an old migraine is still lingering. some days i think i can push 8 hours, and by hour 4 my eyes are sending distress signals. nobody at work sees this calculation. they see me taking breaks, dimming the lights, leaving early.

they don’t see the math every morning. finally logged what actually triggers it: screen time alone isn’t the culprit. it’s screen time + sleep debt + cycle window = migraine by end of shift. anyone else doing this daily math?

how do you figure out your real limit?

ymmv.