“There was always a quest for more minutes, more hours, faster progress to accomplish more in each day. The simple joy of living between summers was gone.”

Published as "A Beautiful Thought … we clip from an exchange paper" in Universalist Union (16 March 1844) this is often quoted as an advertisement originally written by Mann, attributed to him in Getting on in the World (1874) by William Mathews, p. 268; and most publications since that date, and sometimes titled "Lost, Two Golden Hours".
Variants:
Lost,
Two golden hours:
Each with a set of
Sixty diamond minutes!
No reward
Is offered, for they are .
Lost for ever!
Published as "Loss of Time" in The Church of England Magazine (28 June 1856) without any crediting of authorship.
Lost, yesterday, somewhere between sunrise and sunset...
The most commonly quoted variant simply begins with a comma rather than a dash.

Interview at Brown's official site http://www.danbrown.com/novels/davinci_code/faqs.html
Context: Interestingly, if you ask three people what it means to be Christian, you will get three different answers. Some feel being baptized is sufficient. Others feel you must accept the Bible as absolute historical fact. Still others require a belief that all those who do not accept Christ as their personal savior are doomed to hell. Faith is a continuum, and we each fall on that line where we may. By attempting to rigidly classify ethereal concepts like faith, we end up debating semantics to the point where we entirely miss the obvious — that is, that we are all trying to decipher life's big mysteries, and we're each following our own paths of enlightenment. I consider myself a student of many religions. The more I learn, the more questions I have. For me, the spiritual quest will be a life-long work in progress.

As quoted in "Genius at Work" in People magazine, Vol. 43 No. 9 (6 March 1995)

The Glass Bead Game (1943)
Context: It is a pity that you students aren't fully aware of the luxury and abundance in which you live. But I was exactly the same when I was still a student. We study and work, don't waste much time, and think we may rightly call ourselves industrious — but we are scarcely conscious of all we could do, all that we might make of our freedom. Then we suddenly receive a call from the hierarchy, we are needed, are given a teaching assignment, a mission, a post, and from then on move up to a higher one, and unexpectedly find ourselves caught in a network of duties that tightens the more we try to move inside it. All the tasks are in themselves small, but each one has to be carried out at its proper hour, and the day has far more tasks than hours. That is well; one would not want it to be different. But if we ever think, between classroom, archives, secretariat, consulting room, meetings, and official journeys — if we ever think of the freedom we possessed and have lost, the freedom for self-chosen tasks, for unlimited, far-flung studies, we may well feel the greatest yearning for those days, and imagine that if we ever had such freedom again we would fully enjoy its pleasures and potentialities.

Lauren Jauregui on Twitter, Twitter, October 5, 2018 https://twitter.com/LaurenJauregui/status/1048309553199292418,

Source: A machine that learns (1951), p. 63.

Source: The Realm of Possibility