Man’s Origin and Destiny

Sixth, the first day itself consisted of a "Day" and a "Night" — a continuous light period followed by a continuous period of darkness.   Thus the former first-mentioned "day" in Genesis 1:5a was obviously very considerably shorter than the latter "Day" in Genesis 1:5b, of which it was but a part.

Seventh, the days of formation week were days on which great miracles were performed. They could therefore themselves well have been miraculously long or miraculously short days — just as they most certainly were indeed pre-human and therefore non-human days.