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 secrets and compromises. You don't need to carry all that weight. Why don't you set that bag down? Some animals were meant to carry each other, to live symbiotically for a lifetime. Star-crossed lovers, monogamous swans. We are not those animals. The slower we move, the faster we die. (..)2009 Up in the Air
(..) I don't mean to belittle your collection. I get it. It sounds cool. I'd be the th person to do it. More people have walked on the moon. -Do they throw you a parade? -You get lifetime executive status. You get to meet the chief pilot, Maynard Finch. And they put your name on the side of a plane. (..)2009 Up in the Air