I am not familiar with the app. If I were designing an app though, I would have the 10.0 two days BEFORE O, as you are most likely to get pregnant 2 days before O. If you DTD on day of O, it is usually too late as the sperm need time to travel up to the tubes to meet the egg. It's actually best to DTD for 3-5 days before you O, up to O.
I am not sure how the app calculates data, but if it doesn't have many cycles to go off of, or they vary, it could be giving you a large window, or it could just give you a generous window.