And it came to pass at the end of forty days
From the appearance of the mountains, that is, from the first day of the tenth month, to forty days after; and being ended, this must be the eleventh day of the eleventh month, the month Ab, which answers to July and August; and according to Bishop Usher F11 it was Friday the twenty eighth of August:
that Noah opened the window of the ark which he had made;
of which (See Gill on Genesis 6:16).
F11 Ut supra. (Annales Vet. Test. p. 4.)