Charles Ellicott Commentary Exodus 12:41

"And it came to pass at the end of four hundred and thirty years, even the selfsame day it came to pass, that all the hosts of Jehovah went out from the land of Egypt." — Exodus 12:41 (ASV)

The selfsame day ... all the hosts ... went out. — All started, i.e., on one and the same day—the fifteenth of the month Abib. Some would start during the night, some in the morning, others at different periods of the day. They had different distances to traverse in order to reach the appointed halt, Succoth.