“It usually takes me two or three days to prepare an impromptu speech.”
Variant: It usually takes more than three weeks to prepare a good impromptu speech.
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Mark Twain 637
American author and humorist 1835–1910Related quotes

“Churchill has spent the best years of his life preparing impromptu remarks.”
Quoted in A Politician Must Watch His Wit by Clayton Fritchley in The New York Times Magazine (3 July 1960), p. 31

As quoted in The Wilson Era; Years of War and After, 1917–1923 (1946) by Josephus Daniels, p. 624. Referenced in "Bartleby.com" http://www.bartleby.com/73/1288.html
1920s and later

“Give me two hours a day of activity, and I'll take the other twenty-two in dreams.”
Mon Dernier soupir (My Last Sigh, 1983)

“Give me two hours a day of activity, and I'll take the other twenty-two in dreams.”
Mon Dernier soupir (My Last Sigh, 1983)

“Take me or leave me; or, as is the usual order of things, both.”

“Two or three days at sea are equivalent to at least as many weeks on shore.”
Prologue
Tourmalin's Time Cheques (1885)

Heifetz official web site http://www.jaschaheifetz.com/about/quotes.html

“Delighted and frankly amazed that Diana is prepared to take me on.”
BBC News online http://news.bbc.co.uk/onthisday/hi/dates/stories/february/24/newsid_2516000/2516759.stm 'On this day', 24 February 1981.
Interview with the BBC on announcing his engagement to Lady Diana Spencer.
1980s

“Give me three days and three nights of hard fighting, and you will be relieved.”
Statement made by Taylor to the men of Easy Company, 506th Parachute Infantry Regiment, as he circulated among the men on June 4, 1944, two days before commencement of the amphibious invasion of France, Operation Overlord. Easy Company and the entire 101st Airborne Division fought for 7 days, more than twice the promised number, before its last major fight in Normandy at the Battle of Bloody Gulch on June 13. Two days later on June 15, 9 days after the start of Mission Albany, the 101st Airborne's specific part of Overlord, was considered over. As quoted in Band of Brothers (1992) by Stephen E. Ambrose, p. 65