“Jewish time” is a sometimes offensive term for “late.” A similar term is “colored people’s time.” The expressions are sometimes not regarded as offensive if told within that particular ethnic group.
 
“Jewish time” has been cited in print since at least 1927, when it was written in The Daily Worker (New York, NY):
 
“Being acquainted with many Jews, I know that they think that Jewish time is synonymous with ‘late.’”
   
             
Old Fulton NY Post Cards
10 June 1927, The Daily Worker (New York, NY), “Books” by William Pickens, pg. 6, col. 5:
NIGGER HEAVEN, by Carl Van Vechten.
(...)
One finds that Carl Van Vechten thinks that C. P. T. (colored people’s time) is a Negro trait and is synonymous with the word “late”. Being acquainted with many Jews, I know that they think that Jewish time is synonymous with “late.” An observer, therefore, says, “If that is true, there must be a general reason that accounts for that. We see that it is not seemingly only a Negro trait but also a Jewish one. What have those two races in common?”
 
Google News Archive
4 October 1978, The Michigan Daily (Ann Arbor, MI), “Levin running strong” by Keith Richburg, pg. 1, col. 1:
To a rally of the St. Clair County AFL-CIO, Democratic U.S. Senatorial candidate Carl Levin explained that the reason he almost arrived late was because he was running on “Jewish time.” When he was in Israel, Levin explained, he called the telephone number to get the correct time, and the recording said: “At the tone, the time will be 8:00—at the latest, 8:30.”
 
“That’s Jewish time,” Levin said, and as with most of his jokes, the audience only moaned.
 
10 May 1979, The California Courier (Fresno, CA), pg. 8, col. 4:
Ethnic jokes abounded, perhaps best exemplified when, having strode into the room a bit late, he explained that since the difference between arriving 8 AM “Armenian time” and “Jewish time” is “oh, about five minutes,” he knew his timing would be perfect.
 
29 November 1981, The Plain Dealer (Cleveland, OH), “JCC retreat is a morale booster” by Tina Schlatter, pg. 20-C, col. 2:
“So you’re hungry. Oy vey. What can I say. This is Jewish time, one-half hour behind schedule,” laughed a woman eying long lines of people waiting for bagels and blintzes.
 
Google Books
Northern California Jewish Bulletin
Volume 139
1990  
Pg. 118: 
For Sherman, the seder is essentially a spiritual gathering, conducted according to what she calls “Chassidic time, which is even slower than Jewish time.”
   
Google Books
A Life on the Fringe:
The Memoirs of Eugene Forsey
By Eugene Forsey
Don Mills, ON: Oxford University Press Canada
1991  
Pg. 63:
When I told this to a Jewish friend from the West End, he laughed: ‘Don’t you know our saying: “7:30, Jewish time; that means be on hand at 9:00 sharp.”’
 
Google Books
Frommer’s New York ‘91
By Faye Hammel
New York, NY: Prentice Hall
1991
Pg. 103:
Sammy’s serves dinner every night from 4 p.m. to midnight, “Jewish time.” That means maybe a little earlier, maybe a little later.
 
Google News Archive
14 April 1998, Pittsburgh (PA) Post-Gazette, “When to use racial terms a touchy subject,” pg. G-2, col. 2:
Baum said that among his fellow Jews he sometimes uses derogatory terms about Jewish people, joking about jewish time—a reference to being late for appointments—but “I’d find these terms offensive from someone else.”
 
Urban Dictionary
Jewish time
Not perfectly on time; possibly somewhat late, but no harm is done as a result. The implication is that there is no need to be exactly on time, and starting a little late is acceptable.
 
The term comes from Jewish culture, which is often relaxed about punctuality.
 
When an event is schedule to take place at 2:00 Jewish time, it could be at 2:05, 2:12, 2:15, or even 2:35, and everyone is satisfied.
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by Bed time August 09, 2010