now or never

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*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

(it's) now or never

you should do something immediately because you may not get another opportunity Olympic athletes only get a chance to compete every four years, so it's now or never for me.
See also: never, now