it's now or never

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
Farlex Dictionary of Idioms.

*now or never

at this time and no other. (*Typically: be ~; become ~.) This is your only chance, John. It's now or never. I decided that it was now or never, and jumped.
See also: never, now
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

now or never

used to convey urgency.
1994 James Kelman How Late It Was, How Late It's now or never, know what I'm saying; he's out this once, there's no gony be a second time.
See also: never, now
Farlex Partner Idioms Dictionary

it’s ˌnow or ˈnever

you must do something now because you will not get another opportunity to do it: If we don’t climb it now, we never will. It’s now or never.
See also: never, now
Farlex Partner Idioms Dictionary

now or never

Last chance to speak or act. This term goes back to the ancient Greeks and Romans. In English, Chaucer used it in Troilus and Criseyde (“Never er now? what sey ye, no?”) and Shakespeare in Henry VI, Part 2, 3.1: “Now, York, or never, steel thy fearful thoughts.”
See also: never, now
The Dictionary of Clichés by Christine Ammer
See also:
  • now or never
  • now or never, it's
  • no time like the present
  • no time like the present, there's
  • there's no time like the present
  • that's better
  • as good as done
  • good as done
  • good as done, as
  • be done to a turn