Leupold Genesis part 43 verse 13

13. Then came evening, then came morning, --the third day.

On this verse compare above v. 5.

It is true that the first three days have no sun and no moon to furnish and to measure the needed light. But that fact does not in any wise warrant trying to make these days appear as different from the following three or four, for the pattern into which all six days of work fall is consistently the same for all, "then came evening, then came morning." It is the author's purpose by this means emphatically to declare the six days alike as to length and general character regular twenty-four hour days. Nothing but the desire to secure harmony with the contentions of certain physical sciences ever could have induced men to tamper with this very plainest of exegetical results.

Follows the work of the fourth day in v. 14-19.

Since this has to do with the appointment of luminaries, we see, first of all, how this day's work attaches itself to the work of the third day, as well as how it reaches over to the works that are yet to follow. For the vegetation that was brought into being by the work of the preceding day needs not only light but also seasons with modification of light. Consequently, that intricate set of operations that brings seasonal changes for vegetation and for man now appropriately follows.