Zeus and Themis representing either the three seasons, Spring, Autumn and Summer, or else the three ethical attributes of Law, Justice and Peace.
Their name does not thus mean 'hours', or at any rate did not mean this as originally understood for the three. As seasons, the Hours were respectively named Thallo, Carpo and Auxo; as ethical names (in Hesiod) they were Eunomia, Dice and Irene (or Eirene).
The origins of these six names are as follows: Thallo from thallo, 'to bloom', 'flourish'; Carpo from carpos, 'fruit'; Auxo from auxe, 'increase' (the summer is the season of fulfilment) ; Eunomia from eu-, 'good' and nomos, 'law', 'custom'; Dice from dice, 'right', 'order'; Irene from eirene, 'peace'. In his Theogony, Hesiod himself says the three 'watch over' (oreuousi) the works of mortal men - hence their name.