A day & night indicator (normally) turns once in 24 hours. A simple day/night indicator can be a two-colour disc showing day or night through either white and black coloured segments. Mechanically the same as a 24 hour indication, one turn of a hand in 24hours.
Breguet Classique Hora Mundi 5717
Breguet Reine de Naples « Jour/Nuit » (8998)
Dubois Dépraz retrograde seconds, GMT & 24 Hour Indicator module. Reference 15115