“Take out the slaves at the appropriate time” (Psalms 68:7). Rabbi Akiva says: He only took them out in the appropriate month to leave, not in Tammuz – because of the heat, and not in Tevet – because of the cold, but rather in Nissan, which is the appropriate time to start out, not too hot and not too cold – and if you say Tishrei? That is the season of rains.

Bamidbar Rabba, 3