“Now or never was the time.”
Book IV, Ch. 31.
The Life and Opinions of Tristram Shandy, Gentleman (1760-1767)
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Laurence Sterne 50
Irish/English writer 1713–1768Related quotes

“Sometimes there is no next time, no time-outs, no second chances. Sometimes it’s now or never.”

“The time for action is now. It's never too late to do something.”
Quoted as Sandburg in Stop Whining! Start Selling!: Profit-Producing Strategies for Explosive Sales Results (2003) by Jeff Blackman, but without citation of original source; this is elsewhere attributed to Antoine de Saint Exupéry, but also with no original sources cited.
Disputed

“Yeah, but if I don't start my nervous pacing now, I'll never have it all done in time.”
Source: The Republic of Thieves

Introduction to "Be Prepared"
Songs by Tom Lehrer (1953)
Context: I would like to state at this time that I am not now and have never been... a member of the Boy Scouts of America. Their motto is, as you know, "Be Prepared!" and that is the name of this song.