New Defender's Study Bible Notes
2:21 times and seasons. God established the sun, moon, and stars with their motions, to serve for the measurement of time and the establishment of seasons (Genesis 1:14). The great Flood may well have resulted in changes in these. For example, the year may have been 360 days long in antediluvian times (Genesis 7:11,24; 8:4,14), and the distinctiveness of the seasons was probably accentuated by the upheavals of the Flood.
2:21 understanding. See on Daniel 1:17.