Stopping purification at a critical time

In my opinion, today it can be made easier when women walk with their underwear tight to their bodies, it is almost impossible for a woman to bleed without noticing, if she had bled before or would have seen the break or would have seen blood coming out.
All the exactingness about the sunset belonged to times past when a woman was dressed in many layers and it was possible for a drop of blood to come out without her seeing it.
Of course, if during sunset she spent a long time without her underwear, she cannot rely on this permission.

Thanks for the reference!
I saw that the answer there refers to the test being definitely after sunset and different opinions are presented there.
What happens in the case of doubt whether after sunset, in such a case is it possible to give relief even to the opinion of those who forbid?

Another thing, is it possible to know the exact sunset time in the area where I live at the resolution of a street or neighborhood?

Yes, because it is doubtful. And the one who is strict will receive blessings.
I don't know. Just look up tables online.