Sperm lives for up to a week and then we ovulate for around 24 or so hours. You can get pregnant any time during that time. If you are ovulating on a day according to the app, you were fertile a week prior to that and on that day. BUT, do keep in mind that an app is not measuring your hormone levels and is just using numbers to give you an idea. You can ovulate off your normal schedule and, therefore, if having unprotected sex, get pregnant any time during your cycle. good luck