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