The words month and day are ofttimes, for brevity sake, omitted by the Hebrews, as being easily understood. Thus the first of the feast, Matthew 26:17, is the first day of the feast, Mark 14:12.
Related Commentaries of Genesis 8:13
Genesis 8:13
13 And it came to pass in the six hundredth and first year, in the first month, the first day of the month, the waters were dried up from off the earth: and Noah removed the covering of the ark, and looked, and, behold, the face of the ground was dry.