school me on ovulation

Need to clarify some questions. I started using opks last month into my second now. I got a positive yesterday. Was not able to BD all week except Sunday and Monday BBC hubby was away for work. He will be home tonight, shortly!  We plan on BD tonight. My question is if you ovulate within 12-36 hours from a positive opk. Does the egg stay around for an additional 24 hours or so? Or is it just within those 12-36 hours does that make sense? I don't know if I missed my chance!! Thanks so much!