“Buy now—pay later” is a popular sales tactic. “It’s amazing how fast later comes when you buy now!” is a saying that has been printed on many images. Origin of the saying is unknown.
 
“If you want to see time fly, just observe how soon later comes when you buy now” was printed in Ashley Cooper’s column in The News and Courier (Charleston, SC) on August 19, 1966. “Isn’t it frightening how soon later comes when you buy now!—Mary Louise Wild, Louisville” was printed in The Courier-Journal & Times (Louisville, KY) on November 23, 1967. “It’s frightening how soon LATER comes when you buy NOW” was printed in the Trudy comic strip by Jerry Marcus in many newspapers on July 14, 1970.
 
“It’s amazing how fast later comes when you buy now!—Milton Berle” was posted on Twitter by Telemill on April 29, 2008. American comedian and actor Milton Berle (1908-2002) is frequently credited with this version of the saying, but it’s likely that Berle used the existing saying.
 
     
19 August 1966, The News and Courier (Charleston, SC), “Doing The Charleston” by Ashley Cooper, pg. 1-B, col. 1:
If you want to see time fly, just observe how soon later comes when you buy now.
 
3 September 1967, The Courier-Journal & Times (Louisville, KY), “Funnybone,” magazine sec., pg. 12, col. 2:
Isn’t it frightening how soon later comes when you buy now!
Mary Louise Wild,
Louisville
   
Old Fulton NY Post Cards
23 November 1967, Gowanda (NY) News & Observer, “Moose News,” pg. 8, col. 2:
“Isn’t it frightening how soon later comes when you buy now?”
 
10 December 1967, The Sunday Sun (Baltimore, MD), “Sunday Punch,” magazine sec., pg. 39, col. 1:
ISN’T it frightening how soon later comes when you buy now?
 
6 June 1970, Ludington (MI) Daily News, “Case’s Column,” pg. 4, col. 7:
Ever notice how fast later comes when you buy now?
 
14 July 1970, Alton (IL) Evening Telegraph “Trudy” comic strip by Jerry Marcus, pg. B-8, col. 1:
(Trudy is looking at bills that have arrived in the mail.—ed.)
“It’s frightening how soon LATER comes when you buy NOW.”
 
25 August 1973, Courier-Post (Camden, NJ), “It happened Last Night” by Earl Wilson, pg. 33, col. 7:
REMEMBERED QUOTE: “Isn’t it frightening how soon Later comes when you buy Now?”
   
5 December 1993, The Press Democrat (Santa Rosa, CA), “Scram-lets” edited by Clay R. Pollan, pg. F4, col. 4:
After going over the monthly bills, the husband turned to his wife and mumbled, “I didn’t realize how fast later comes when you buy now.”
   
Google Books
March 1997, The Rotarian, “Stripped Gears,” pg. 64, col. 1:
Did you ever notice…
. how quickly “pay later” comes when you “buy now”?
   
Twitter 
Telemill
@Telemill
It’s amazing how fast later comes when you buy now!—Milton Berle
12:48 PM - 29 Apr 2008
   
26 November 2008, The Sun (London, UK), “The bloke quote” by Jane Moore, pg. 11:
IT’S amazing how fast later comes when you buy now
- MILTON BERLE
 
Google Books
Instant Wealth Producing Home-Based Business Plans with Selected Money Thoughts by the Rich and Famous:
A Preliminary Guide
By Dr. Beatrice Batnag Donofrio and Mr. Antonio R. Batnag Donofrio
Xlibris Corporation (Xlibris.com)
2009
Pg. 313:
“It’s amazing how fast later comes when you buy now!” Milton Berle
 
Twitter
Hibernian Financial
@HibernianFP
“It’s amazing how fast later comes when you buy now!” - Milton Berle #WisdomWednesday
7:01 AM - 13 Mar 2019