What would you count as day 1?

Trying to track because I'm heading out of town for work at the end of my fertile window. I think this is our last window of TTC before I do the testing for

IVF

as hubs may be sterile from a medicine he has to take which means Im supposed to start BC 😑 ...

My cycle was set to start Thursday. Wednesday night i got home from a work dinner at 10 pm, I had red blood, not heavy, just when I wiped. Was crampy so I put in my cup. It had some blood in there in the AM. My cycle was heavy by Thursday afternoon. Friday i did labs. Would you count Wednesday as cycle day 1 or Thursday?