on borrowed time

In a temporary and/or tenuous position, which will likely come to an end suddenly and abruptly. The company has been on borrowed time ever since those risky investments in 2007 went sour. Accidents and disease can strike so unexpectedly that it feels like we're all existing on borrowed time.

borrowed time, on

An unexpected extension of time. It often refers to someone terminally ill or in great danger but surviving longer than was anticipated, on time that is in effect borrowed from Death. The term dates from the late 1800s. Raymond Chandler used it in The Big Sleep (1930): “Brody was living on borrowed time.” James Patterson also had it, referring to the 48-hour deadline for a threatened bombing attack: “We were definitely operating on borrowed time” (London Bridges, 2004).