your ticker is just an average based on your cycle length. Doesn't mean it is exact. Everyone's bio is different. I wouldn't solely base your O time on just the estimates

Weren't some of your last cycles were off by a few days, so that can mean you O'd different times. Some women are like clockwork though, I wish my cycles were

The more data you have is best, and I think the CBFM is really really helpful!