now or never, it's

now or never

At the current time or not at all. Said of an action that must be done now or will not be able to be done in the future. Once we start our careers, it will be harder and harder to take a backpacking trip like this. It's now or never! If you have to go to the bathroom before we get back on the road, go now, because it's now or never!
See also: never, now

now or never, it's

It must be done now or not at all, as in If you plan to state your case to the boss, it's now or never. This phrase was first recorded in 1560.
See also: now