What does 1 Kings 16:23 mean?

Omri became king of Israel in the thirty-first year of Asa’s reign over Judah. He ruled for twelve years, six of those from Tirzah. 1 Kings 16:23 - Modern Text Bible

(Omri’s reign is longer and more stable than his predecessors. The timeline is again anchored to Asa’s reign in Judah.)