I can actually answer this from my perspective as a cinematographer. "Light" and "Dark" are relative terms when it comes to our perception, or "exposure". There's something that we can agree to be "absolute dark", or 0 LUX when measured by a light-meter device. Every progressive gradation of "light" would then be a "non-zero LUX" measurement. Hence we have an absolute darkness, and progressively brighter settings. The difference between night time and day time is around 30,000 lux.
You can read up on it here:
https://en.wikipedia.org/wiki/Lux
When you ask me as to when it stops being dark and starts being light during the sunrise phase, I'll have to ask you as to what you consider to be "light". Is it the full sunrise at "400 lux"? Well, then it's fairly straightforward. I'll pull out a lightmeter and a watch and clock the exact time when we hit "400 lux" during the sunrise phase.
Your issue here is with your refusal to identify as to when you would consider someone a person on a certain continuum, because it allows you to evade this question all together.
So, let's begin with a very simple scenario. Would you consider a newborn a person?