it’s now or never
From Longman Dictionary of Contemporary Englishit’s now or neverit’s now or neverCHANCE/OPPORTUNITYused to say that if someone does not do something now, they will not get another chance to do it Quite suddenly, her mind was made up. It was now or never. → nowExamples from the Corpusit’s now or never• Twoflower, I thought, it's now or never.