A popular “dumb blonde” joke demonstrates how long it takes a blonde to process a joke. The St. Louis (MO) Post-Dispatch, on August 14, 1991, had this as just a day:

Q: How do you make a blonde laugh on Friday?
A: Tell her a joke on Thursday.

The Houston (TX) Chronicle, on August 27, 1991, had this as the entire weekend:

Q: How do you make a blonde laugh on Monday?
A: Tell her a joke on Friday.

A popular form, published in The Arizona Republic (Tucson, AZ) on September 6, 1991, indicates that a Saturday date needs several days of preparation:

Q: How do you make a blonde laugh on Saturday?
A: Tell her a joke on Wednesday.


14 August 1991, St. Louis (MO) Post-Dispatch, “A Light-Headed Minority THat’s Heavy On Jokes” by Elaine Viets, pg. 3E, col. 5:
Q: How do you make a blonde laugh on Friday?
A: Tell her a joke on Thursday.

27 August 1991, Houston (TX) Chronicle, “Blondes Have More Dumb/Once objects of adoration and envy, today’s blondes are taking a bashing” by Michele Meyer, pg. 1:
Q: How do you make a blonde laugh on Monday?
A: Tell her a joke on Friday.

10 October 1991, The Times (Trenton, NJ)< "No kidding, tell blondes to lighten up" by Brenda Brissette-Mata, pg. A23, col. 4:
Q. How do you make a blonde laugh on Monday?
A. Tell her a joke on Friday.

6 September 1991, The Arizona Republic (Tucson, AZ), “29 Blonde Jokes,” pg. E12, col. 5:
Q: How do you make a blonde laugh on Saturday?
A: Tell her a joke on Wednesday.

Google Groups: rec.humor
Blonde jokes (list)
bu...@ac.dal.ca
9/21/91
(...)
17. How do you make a blonde laugh on Monday?
(Tell her a joke on Friday)

5 October 1991, Orlando (FL) Sentinel, “Blondes laugh off the latest trend in jokes” by Martha Sherrill, pg. E1:
How do you get a blonde to laugh on Saturday? Tell her a joke on Tuesday.

Google Books
Kudzu Don’t Cover Everything
By Bo Whaley
Nashville, TN: Rutledge Hill Press
1993
Pg. 100:
How do you make a blonde laugh on Monday? Tell her a joke on Friday.

Google Groups: rec.humor
Canonical List of Blonde Jokes (was Largest List of Blonde Jokes)
Belding, Troy C.
8/31/93
(...)
Q:  How do you make a blonde laugh on Saturday?
A:  Tell her a joke on Wednesday.

Google Books
Unbelievably Gross Jokes, Volume XXVII
By Julius Alvin
New York, NY: Kensington Publishing Corporation
1998
Pg. 1:
How do you make a blonde laugh on Saturday?
Tell her a joke on Wednesday.

Google Books
Adult Only Blonde Jokes:
Guaranteed to make you giggle!
Dingley, Victoria: Hinkler Books
2004
Pg. 195:
Q. How do you make a blonde laugh on a Monday?
A. Tell her a joke on a Friday.

Google Books
Penguin Pocket Jokes
By David Pickering
London, UK: Penguin Books
2006
Pg. ?:
How do you make a dumb blonde laugh on Monday morning?
Tell her a joke on Friday night.

Google Books
The Ultimate Book of Blonde, Brunette, and Redhead Jokes
By James Buffington
Berkeley, CA: Ulysses Press
2010
Pg. 18:
How do you make a blonde laugh on Friday?
Tell her a joke on Monday.

Twitter
Laffy Taffy Jokes
@Laffy_TaffyJoke
How do you make a blonde laugh on Saturday?
Tell her a joke on Wednesday.
1:02 AM - 19 Feb 2014

YouTube
Jokes - How can you get a blonde to laugh on Saturday? Tell her a joke on Wednesday.
jokesus
Published on Oct 2, 2015
Joke :
How can you get a blonde to laugh on Saturday?
Tell her a joke on Wednesday.

Google Books
Blonde Jokes
By Joe King
Marine Publishing
2016
Pg. ?:
Q: How can you get a blonde to laugh on Saturday?
A: Tell her a joke on Wednesday.