John Gill Commentary 1 Kings 15:33

"In the third year of Asa king of Judah began Baasha the son of Ahijah to reign over all Israel in Tirzah, [and reigned] twenty and four years." — 1 Kings 15:33 (ASV)

In the third year of Asa king of Judah began Baasha the son of
Ahijah to reign over all Israel in Tirzah
Which is repeated, partly to observe that the whole kingdom submitted to him, though an usurper and murderer, and the place where he kept his court, as also the time of his reign, as follows:

twenty four years ;
which were as long as both Jeroboam and his son reigned.