“A rule to live by: I won't use anything I can't explain in five minutes.”

Source: Shadowfever

citation needed
The Late Late Show with Craig Ferguson (2005–2014), Commonly repeated

There is no indication that Einstein said this. According to Quote Investigator, the earliest publication of a quote similar was in a collection of articles about manufacturing in 1966, when an employee of the Stainless Processing Company wrote a piece titled "The Manufacturing Manager's Skills." The article attributed the quote to an unnamed professor at Yale, by saying, "If I had only one hour to solve a problem, I would spend up to two-thirds of that hour in attempting to define what the problem is." (See, 1966, The Manufacturing Man and His Job by Robert E. Finley and Henry R. Ziobro, "The Manufacturing Manager's Skills" by William H. Markle (Vice President, Stainless Processing Company, Chicago, Illinois), Start Page 15, Quote Page 18, Published by American Management Association, Inc., New York. Verified on paper). https://quoteinvestigator.com/2014/05/22/solve/
Disputed
Variant: If I had an hour to solve a problem I'd spend 55 minutes thinking about the problem and 5 minutes thinking about solutions.

After receiving the Best Picture Oscar for "Lord of the Rings: The Return of the King" at the 76th Academy Awards

Pedantic & Whimsical (2006)

Source: The Dark Tower

July 3, 1998 Denver Post column

Source: Watchmen