I'm very confused about the fertile window and the ovulation day. I've heard that there is a 12-24 hr period in which you can get pregnant and that's it, is that true? If so, why does <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> say we have a fertile window for a week? Is it possible to get pregnant at any time or just in the time you're fertile?