1)
Were the donkeys lost for three days?
1.
Radak citing Targum Yonasan: No. Today makes three days that you are seeking them.
2)
Why did he say "ul'Mi Kol Chemdas Yisrael"?
1.
Rashi: He hinted to him about the kingship
2.
Malbim: This is a second reason not to be concerned for the donkeys. [They were found, and] to whom are all desired matters of Yisrael? [To you!]