“Two weeks to change the world, fourteen days to destroy it.”

"Prof. Huxley Predicts 2-Day Working Week" The New York Times (17 November 1930) p. 42
Context: Some day no one will have to work more than two days a week... The human being can consume so much and no more. When we reach the point when the world produces all the goods that it needs in two days, as it inevitably will, we must curtail our production of goods and turn our attention to the great problem of what to do with our new leisure.

Prologue
Tourmalin's Time Cheques (1885)

A humorous personal mantra he used to combat his states of depression, published in Too Soon to Say Goodbye (2006)
Leaving Home (1995).

Source: An Introduction To Probability Theory And Its Applications (Third Edition), Chapter II, Elements Of Combinatorial Analysis, p. 32.

A Leaf of Spearmint, III
Little Rivers http://www.gutenberg.org/dirs/etext98/ltrvs10.txt (1895)

Arthur's commentary
The Nemesis of Faith (1849)
Context: Our characters change as world eras change, as our features change, slowly from day to day. Nothing is sudden in this world. Inch hy inch; drop by drop; line by line. Even when great convulsions shatter down whole nations, cities, monarchies, systems, human fortunes, still they are but the finish, the last act of the same long preparing, slowly devouring change, in which the tide of human affairs for ever ebbs and flows, without haste, and without rest.

Source: Dear John

In an "Ephemera" blog post http://kfmonkey.blogspot.com/2009/03/ephemera-2009-7.html
This also appears in Ch. 10 of The Value of Nothing (2010) by Raj Patel, who later acknowledged it was a borrowed joke in "Citation Alert!" http://rajpatel.org/2010/01/21/citation-alert/ (21 January 2010) at rajpatel.org.

Source: Hey Nostradamus!