That hadeeth has many narrations with lots of different wordings, it explains itself in another narration by saying: "I alternate the night and the day".
What it means is that do not swear time*, because it is only a creation of Allaah and can do nothing of its own accord, so when you swear it then you are actually swearing Allaah because it is Allaah who is causing that thing to happen.
When any calamity like death or loss of wealth etc used to befall the mushrikeen they used to say: "Yaa khaybatad dahr", which means something like "Oh useless time!"
So Rasoolullaah Sallallaahu 'Alayhi wa sallam said in this hadeeth not to swear time, because by doing so you are swearing Allaah who is the actual One that is controlling the time.