Girls, What do you count as the first day of you're period when it's light?

LayLay96
I've always been wondering this, since it's hard to determine between just spotting and an actual period especially when you're flow starts off in a light way or in a spotting type of way. And what if you start at 4pm or 5pm something like that more towards the evening? Or the afternoon at like 1 or 2pm instead of morning... Which day do you count as day 1 then, the next day or the same day it's happening on? I'm confused and I have a period tracking app also don't know when to mark as the first day...
Girls, What do you count as the first day of you're period when it's light?
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