A Day on Earth Used to Only Be 19 Hours

There is interesting correspondence about this between Newton and Burnet, as documented by Gould in his 1987 "Time's arrow, Time's cycle":

Newton suggested to Burnet that "the paradox of creation in but six days might be resolved by arguing that the earth rotated much more slowly then, producing a "day" of enormous extent."

To which Burnet incredulously responded "But if the revolutions of the earth were thus slow at first, how came they to be swifter? From natural causes or supernatural?"

Burnet also objected that long early days would stretch the lives of patriarchs even beyond the already problematical 969 of Methuselah and his compatriots—and that while organisms might enjoy sunny days of such extended length, the long nights might become unbearable: "If the day was thus long what a doleful night would there be".