“Sleep on it” (not make an immediate decision)

To “sleep on it” is to put off a decision, often with a night to think about it and with an answer forthcoming the following morning. “Resolve to buy a bottle, and don’t ‘sleep on it’” was cited in print in American newspaper advertisements in 1867.
 
“Don’t sleep on it”—the negative form—is often used in advertisements, cautioning a potential customer not to delay in accepting an offer.
 
   
The Free Dictionary
sleep on it
to not make an immediate decision about a plan or idea, but to wait until the next day in order to have more time to think about it.
     
Newspapers.com
13 June 1867, New York (NY) Herald, pg. 5, col. 6 ad:
“BLESSED BE THE MAN WHO FIRST INVENTED Sleep,” saith Sancho Panza. Sleep has often been “murdered,” not in Macbeth’s case only, but in many modern instances by indigestion, nervous disorders, headache and a host of other complaints. For all such there is now a remedy, and sufferers may now proclaim, “Blessed be the man who invented the PLANTATION BITTERS.” This delicious Cordial and Fine Tonic is now hailed by millions as the Great Health Giver and Restorer. Resolve to buy a bottle, and don’t “sleep on it.” “Be wise in time.”
 
10 August 1867, Logansport (IN) Weekly Journal, pg. 3, col. 5 ad:
Resolve to buy a bottle, and don’t “sleep on it.”
(Plantation Bitters—ed.)
         
Chronicling America
22 May 1909, Daily Arizona Silver Belt (Globe, AZ), pg. 8, col. 1 ad:
Now don’t sleep on your opportunities, but start your buying today.
(Brown’s store.—ed.)
 
27 June 1925, The Herald (Miami, FL), pg. B3 classified ad:
Act quick; don’t sleep on it; time will make it cost more.
(Paul Schroeder & Co. - ed.)
 
AZLyrics
MEAT LOAF LYRICS
“Paradise By The Dashboard Light” (1977)
(...)
[Boy:]
Let me sleep on it
Baby, baby, let me sleep on it
Let me sleep on it
And I’ll give you an answer in the morning
 
Urban Dictionary
sleep on it
the act of being lazy, and putting things off.
taking things lightly, and too casually.
to sleep on it
i told her she has to take the cat to the vet, but she sleeps on it
by neveryoumind February 17, 2005
 
ScienceDaily
Complex Decision? Don’t Sleep On It
Date: August 11, 2008
Source: University of New South Wales
Summary:
Neither snap judgements nor sleeping on a problem are any better than conscious thinking for making complex decisions, according to new research. The finding debunks a controversial 2006 research result asserting that unconscious thought is superior for complex decisions, such as buying a house or car. If anything, the new study suggests that conscious thought leads to better choices.
 
Twitter
Mohamed Ndiaye
‏@TribalM0
My album drops 2015 don’t sleep on it
12:31 AM - 27 Dec 2014