Once you start to ovulate how long do u have until it's not able to be fertallized?

Varies: Viability of the egg varies due to many factors, but most estimate about a 24-48 hour window.

24 hours or less: An oocyte can be fertilized for a maximum of 24 hours after ovulation, many believe only 10-12 hours. Technically that's not quite the same as saying 24 hours after detection of an lh surge. It's much shorter than most realize, the idea of "4-5 fertile days" is not biologically correct at all, it's a simplification for timing strategy at home.