borrowed time, on

An uncertain length of time that may end soon or suddenly, bringing any activity, situation, or fortunes associated with it to an end as well. Usually refers to the final period of one's life, in the form "living on borrowed time." In the scope of the planet's history, human existence is a tiny blip and unlikely to last forever—just borrowed time, really. Accidents and disease can strike so unexpectedly that it feels like we're all living 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.

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).