When to mark Period Start in Glow

Angela • 💍 Married 10-11-12! 👫TTC since 11/2013. 💉 IVF #1: 6/2016, miscarried 7/2016. 💉 IVF #2: 8/2017, miscarried 10/2017. 🌈 FET #1: 4/2018, Rowan Amelia born 12/16/18
AF due CD27. 
Did the BD on CD25. Bled a little, so I thought AF had shown her ugly face early. Nope just a little spotting. CD26 & 27 a little spotting. But today, CD28 AF is def here. 
Question is, how do I properly enter my AF on Glow? Did it start when I first started spotting? Or is it when it's def here? I don't want to be entering wrong dates that could cause my ovulation dates to be inaccurate.