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 I'm bleeding your love When you're swimming in my veins You got me now Been waiting for a lifetime for ya Been breaking for a lifetime for ya Wasn't looking for love till I found you Oh, na-na-eh (..)2018 Fifty Shades Freed
(..) - Oh, my God. You wanted to see more of your friends. - : Come here. - You guys! Been waiting for a lifetime for ya Been breaking for a lifetime for ya Wasn't looking for love till I found you (..)2018 Fifty Shades Freed