Sforno on Numbers 9:21/ספורנו על במדבר ט׳:כ״א

1ויש אשר יהיה הענן מערב עד בוקר, this is the fourth time that the manner in which the cloud operated is being mentioned, to show that it was impossible to predict with any degree of probability how long they would stay in one location. Sometimes, only overnight. This was not even time enough to pitch their tents, much less to erect the Tabernacle. The principal reason this detail was mentioned is to make clear that the journeys never started at night.