Or HaChaim on Numbers 9:20/אור החיים על במדבר ט׳:כ׳

1 ויש אשר יהיה הענן ימים מספר, Sometimes the cloud would remain over the Tabernacle only for a few days, etc. This too reflects credit on the Israelites. It tells us that although the Israelites had only just made camp they did not demur when they had to move again so shortly thereafter. The verse goes on to repeat that they camped at the command of G'd and that they moved at the command of G'd. The two statements are not to be understood sequentially. All the Torah wants to tell us is that just as the making of camp occurred at the command of G'd so the act of breaking camp occurred at the command of G'd. In either case the Israelites were in full accord with G'd's wishes in the matter, no matter that they had only had a few days' rest between journeys.

2I have noted that Targum Yonatan ben Uzziel translates the words ימים מספר to mean "seven days." If we accept his words we cannot say, as we did, that our verse meant to compliment the Israelites as they had seven days to recover from the effects of their journey. According to Yonatan ben Uzziel we must explain our verse as follows: the Israelites did not demur during encampment or when the time came to break camp although they would have chosen a different time-table for their journeys had they been consulted. They did what G'd said without protest. This is why the Torah emphasised the words על פי ה׳ יחנו ועל פי ה יסעו׳.