now or never
Also found in: Acronyms, Wikipedia.
*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.
(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.