Adam Clarke on Genesis 13:14

The Lord said unto Abram - It is very likely that the angel of the covenant appeared to Abram in open day, when he could take a distinct view of the length and the breadth of this good land. The revelation made Gen 15:5, was evidently made in the night; for then he was called to number the stars, which could not be seen but in the night season: here he is called on to number the dust of the earth, Gen 13:16, which could not be seen but in the day-light.