“What time is it when you sit on a tack?”/“Spring time.”

A time riddle is:
 
Q: What time is is when you sit on a tack?
A: Spring time.
 
The joke has been cited in print since at least 1968. “What time is it when you sit on a pin?”/“Spring time” has been cited in print since at least 2009.
 
     
Google Books
Jokes, Puns, and Riddles
by David Allen Clark
Illustrations by Lionel Kalish
Garden City, NY: Doubleday
1968
Pg. 160:
Question: What time is it when you sit on a tack? Answer: Spring time.
     
24 March 1973, Xenia (OH) Daily Gazette, “Mini Jokes,” The Mini Page, pg. 4, col. 1:
Q. What time is it when you sit on a tack?
A. Spring time.
Dana Wilburn—Xenia
 
16 June 1973, Stamford (CT) Advocate, “Mini Jokes,” The Mini Page, pg. 4, col. 1:
Question: What times is it when you sit on a tack?
Answer: Spring time.
Jimmy Wenning, Age 9, Stamford
 
Google Books
January 1976, Boys’ Life, “Think & Grin,” pg. 74, col. 1:
Hi: What time is it when you sit on a tack?
Jinks: Spring time! — Russell Johnson, Cuyahoga Falls, Ohio.
 
Google Groups: chaopsych
”...imposing a stable, organised state on a chaotic system.”
Frederick D Abraham
10/1/13
(...)
> What time is it when you sit on a tack?
> Spring time.