“People talk vaguely about the innocence of a little child, but they take mighty good care not to let it out of their sight for twenty minutes.”

Source: How to Become President (1940), Ch. 1 : Government jobs pay big money
Context: Who am I to talk? That’s a fair question, and one which deserves a better answer than I can give you. … Come to think of it, who are you? Whoever you are, I sympathize with you. I sympathize with everybody; that’s what I get for being a candidate myself. Let them call us nonentities. Who cares? A nonenitiy can be just as famous as anybody else if enough people know about him.
But let’s leave personalities out of this and just talk about me.

A la Scala, il est d'usage de ne faire durer qu'une vingtaine de minutes ces petites visites que l'on fait dans les loges.
Source: La Chartreuse de Parme (The Charterhouse of Parma) (1839), Ch. 6

Light (1919), Ch. XIV - The Ruins

"Little Things" in the Myrtle (1845). This poem came to be published uncredited as a children's rhyme and hymn in many 19th century magazines and books, sometimes becoming variously attributed to Ebenezer Cobham Brewer, Daniel Clement Colesworthy, and Frances S. Osgood, but the earliest publications of it clearly are those of Carney, according to Our Woman Workers: Biographical Sketches of Women Eminent in the Universalist Church for Literary, Philanthropic and Christian Work (1881) by E. R. Hanson, as well as Familiar Quotations 9th edition (1906) edited by John Bartlett, The Oxford Dictionary of Quotations (1999) by Elizabeth Knowles and Angela Partington, and The Yale Book of Quotations (2006), ed. Fred R. Shapiro.

Animal Dreams.
Animal Dreams (1990)

1747
Letters to His Son on the Art of Becoming a Man of the World and a Gentleman (1774)
Variant: I recommend you to take care of the minutes: for hours will take care of themselves.

From books
Source: Jean Vanier, Community And Growth, 1979

Source: The Master of Go (1951), Ch. 18, p. 76.