John Gill Commentary Numbers 9:18

"At the commandment of Jehovah the children of Israel journeyed, and at the commandment of Jehovah they encamped: as long as the cloud abode upon the tabernacle they remained encamped." — Numbers 9:18 (ASV)

At the commandment of the Lord the children of Israel
journeyed
Or "mouth of the Lord"; not that there was any command in form given, or any audible voice heard, directing when to march; but the removal of the cloud was interpretatively the order and command of God for them to move also:

and at the commandment of the Lord they pitched ;
their tents; when the cloud stopped, they understood that as a signal to them, as a token of the will of God that they should stop likewise; it was to them as an authoritative command, which they obeyed:

as long as the cloud abode upon the tabernacle, they rested in their
tents ;
whether a longer or a shorter time, as is after expressed.