Why did Bil'am ask them to wait specifically overnight for a reply?
Rashi: as we find by Lavan in Vayeitzei Bereishis, 31:24.
Rashi: This can be compared to a king, who goes to his concubine secretly.
What did Bil'am have in mind when he said "Ka'asher Yedaber Hashem eilai"?
Rashi: He thought that Hashem may not allow him to go with men of inferior standing such as them. 1
Seforno: He meant that he needed to prepare himself for prophecy.
What made Bil'am think that Hashem would appear to him upon request (a privilege that was reserved for Moshe Rabeinu, the master of all prophets)?
Oznayim la'Torah: Bil'am was sure that, since the issue concerned Am Yisrael, Hashem would be bound to answer him, because, otherwise, he would go and curse them without permission on the excuse that he tried to obtain His consent but He did not respond. 1
What happened to the elders of Midyan?
Rashi: Refer to 22:7:1:2.
Ramban #1 (in Pasuk 13): When Bil'am informed them that he needs permission from Hashem to curse Yisrael, they left because they knew that Hashem, who took them out of Egypt and who performed with them miracles and wonders, would never grant him the permission that he sought.
Ramban #2 (in Pasuk 13): It seems that the elders of Midyan 1 came to see Balak in Mo'av to discuss with him the sudden appearance of Yisrael, and when they left, Balak sent his wise men together with them to invite Bil'am. When they arrived in Midyan, which was en route to Aram Naharayim, where Bil'am lived, the elders of Midyan remained and the elders of Mo'av continued alone on their way to Bil'am.
Da'as Zekenim (in Pasuk 8): When Bilam mentioned that he required Hashem's consent, they knew that their mission was doomed, since Yisrael are Hashem's children, and a father does not hate his son, so they left. 2
Why did the elders of Midyan leave and not the elders of Mo'av?
Rashi: Refer to 7:2:1:2. It seems that the elders of Midyan knew Bil'am better than the elders of Mo'av.
Da'as Zekenim: Refer to 22:8:3:4. It seems that, Moshe having lived in Midyan. the elders of Midyan were more conversant with the relationship between Hashem and Yisrael than the elders of Mo'av.
Oznayin la'Torah: Moshe having lived in Midyan, the elders of Miyan knew that Hashem was the G-d of Yisrael and that He would never consent to curse Yisrael, only they hoped that Bil'am had the ability to act independently of Hashem. Consequently, when they heard that Bil'am needed Hashem's consent, they left. The elders of Mo'av on the other hand, did not know that Hashem was the G-d of Yisrael. They therefore thought that He might give His consent to curse Yisrael.
