Definition of "hour"

During the whole time of his abode in the university he generally spent thirteen hours of the day in study; by which assiduity besides an exact dispatch of the whole course of philosophy, he read over in a manner all classic authors that are extant […]

1661, John Fell, The Life of the most learned, reverend and pious Dr. H. Hammond‎

It is never possible to settle down to the ordinary routine of life at sea until the screw begins to revolve. There is an hour or two, after the passengers have embarked, which is disquieting and fussy.

1915, G[eorge] A. Birmingham [pseudonym; James Owen Hannay], chapter I, in Gossamer, New York, N.Y.: George H. Doran Company

[Isaac Newton] was obsessed with alchemy. He spent hours copying alchemical recipes and trying to replicate them in his laboratory. He believed that the Bible contained numerological codes. The truth is that Newton was very much a product of his time.

2014 June 21, “Magician’s brain”, in The Economist, volume 411, number 8892

From childhood's hour I have not been / As others were; I have not seen / As others saw; I could not bring / My passions from a common spring.

c. 1829, Edgar Allan Poe, “Alone”, in (Please provide the book title or journal name)‎

Now will be a good hour to show you Milly Erne's grave.

1912 January, Zane Grey, chapter 3, in Riders of the Purple Sage […], New York, N.Y., London: Harper & Brothers Publishers

By 1300 hours the position was fairly clear.

2000, T. C. G. James, edited by Sebastian Cox, The Battle of Britain