Period started spotting at night: what day did it start?

I asked this question in a different way, but I hope to get some more opinions as everyone seems to say something different. I noticed some spotting on toilet paper last night around 8:30pm. When I woke up AF was in full flow! When would you say my period started? I was really stressed this cycle because AF was 2 or 3 days late (she never is--I'm usually like clockwork: 25-26 days.) As this is my first cycle being late, I want to get the date right. Thanks for your help!