What to put on calendar if period comes at night?

Hi Ladies! Well this week was a helluva week. I had a huge pregnancy scare. But luckily last night I started spotting I guess around 8:30pm. This morning I woke up with regular flow. What should I put in the calendar for my start date?  It's got my cycles all messed up now since I usually have a 25/27 day cycle and this one was a 29 day. :/