On Mon, 3 Dec 2018 10:56:51 -0800 (PST), Quadibloc
wrote:
. Earth's day (or rotational period) is exactly 23.9345 hours (or,
23 hours=
, 56 minutes, 4.2 seconds).

No. A sidereal day is 23h 56m 4.09054s and even this value is not
exact but only approximate.