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Webster 1913 Edition

Noun.

(Naut.)

A half watch; a watch of two hours, of which there are two, the first

dogwatch

from 4 to 6 o’clock, p. m., and the second

dogwatch

from 6 to 8 o'clock, p. m.

Totten.

Noun.

Among seamen, a watch of two hours. The dogwatches are two reliefs between 4 and 8 oclock, P.M.

See also: dog watch

dogwatch ‎(plural dogwatches)

(nautical) Aboard a ship, either of the two short two-hour watches that take place between 4 p.m. and 8 p.m.
- 1924, Herman Melville, Billy Budd, London: Constable & Co., Chapter 12,
  […] in the last dog-watch when the drawing near of twilight induced revery […]
(by extension) A night shift, or other very late or early period of duty.
- 1946, Mezz Mezzrow & Bernard Wolfe, Really the Blues, Payback Press 1999, p. 22:
  The girls we knew were all on the dogwatch, from four to twelve in the morning.

nautical: short watch