Or HaChaim on Numbers 9:21/אור החיים על במדבר ט׳:כ״א

1 ויש אשר יהיה הענן מערב עד בקר, Sometimes the cloud remained stationary only from evening to the following morning, etc. From this point on the Torah tells us only about the different periods the Israelites stayed in one place. It commences with telling us about their making camp in the evening, i.e. מערב עד בקר, from evening till morning. Following this we are told that the cloud remained stationary for a day and a night; this is followed by a description of the cloud remaining in one place for 2 days, i.e. יומים. The next longer period was a month, i.e. חדש, followed by ימים, a period of a whole year when the cloud did not move and the Israelites remained in the same spot. This paragraph cannot be meant to convey something similar to the previous verses as there would have been no logical reason to first describe the cloud as remaining stationary for ימים מספר, "a number of days, etc." Such a description should have been mentioned after מערב עד בקר and not before. The expression ימים מספר is to be understood like a general heading for the subject matter, the details following in verse 21-22. There can be no doubt that the first two verses were meant to compliment the conduct of the Israelites throughout most of their long journey through the desert, whereas the last 3 verses described the various lengths of time the Israelites stayed in one place during those journeys. According to the Kabbalists the reason why the Israelites did not break camp at regular intervals was that the purpose of traversing these various areas was to locate and rescue stray sparks of sanctity which had been "captured" by forces resident in this unfriendly desert environment. Only G'd Himself was able to determine which time frame was sufficient for this task to be accomplished in the various locations.