This is the opportunity 'of a lifetime'. = This sort of opportunity comes along 'once in a lifetime'. [=this is a very rare opportunity]
a baseball player's 'lifetime' batting average [=batting average measured over a baseball player's full career]
She was presented with a 'lifetime' achievement award. [=an award for all the work she has done in her life]
(..) And now you will join her. I needed a moment alone with you. - You're insane. - Just answer me this... is a little bit of happiness better than a lifetime of anything else? Answer the question. Yes. - Ready... - I'm gonna hold you to that. (..)2016 TvShow: 12 Monkeys Title: Lullaby Season: 2 Episode 8
(..) Mm-hmm. Thanks, but I only had a few years left, anyway. Yeah, but in those years, you could have found some real happiness. That's better than a lifetime of this. We've been through this. My life is my life, my choices. I didn't have to go to that hotel and wait for you, but I did. (..)2016 TvShow: 12 Monkeys Title: Lullaby Season: 2 Episode 8