The first day of a full flow is considered as your cycle day 1
Yes, your first day is when you see actual red blood loss
The first day of full flow before midday is what I was told
I was told by my clinic if your actual flow starts before 4pm, then that is your cycle day 1. However, if actual flow starts after 4pm the next day is considered your cycle day 1.
It is the first day of full flow 🙂