the selfsame day: i.e. the fifteenth day of the seventh month. The years of the solar cycle show that it was the day that Abraham left "Ur of the Chaldees".
Related Commentaries of Exodus 12:41
Exodus 12:41
41 And it came to pass at the end of the four hundred and thirty years, even the selfsame day it came to pass, that all the hosts of the LORD went out from the land of Egypt.