be just a matter of time

To be an inevitability or eventuality; to be or seem sure to happen at some point in the future. With your reckless spending behavior, it's just a matter of time before you go broke. We'll catch the person responsible eventually. It's just a matter of time. Zack and Ashley have always been crazy about each other, so it's just a matter of time until they get engaged.

it’s only, just, etc. a matter/a question of ˈtime (before...)

used to say that a thing will definitely happen in the future, although it may not happen immediately: Don’t worry, you’ll get a job if you keep looking. It’s just a matter of time. ♢ It’s only a question of time before the fighting spreads to the city.