This song is about the state of confusion that comes from seeing your friends getting married. Vocalist and lyricist Charlie Fink explained to The Daily Telegraph: "'Lifetime' was a reminder for me that I spend so much time on the road, and so much time away from London, that when my friend said he was getting married I became aware of how much I had drifted from my friends, and how little I knew what was going on in anyone's lives."
This was the first song written for Heart of Nowhere. Charlie Fink told Q magazine that the song's subject matter of a friend of his getting engaged was where the inspiration for the whole record started. He explained: "A lot of the album is about the end of adolescence and memories of friendship. We'd come back from tour and find out s--t has changed since we were last here. I found myself at that point in life where you're becoming an adult. That was the starting point for the record."
The bedrock of David Guetta's Nicki Minaj-featuring single "Hey Mama" is a sample of "Rosie," a 1940s prison recording from folk archivist Alan Lomax that songwriter Esther Dean first showed the French DJ on YouTube.