11 Pa.C.S. § 11202

The mayor shall be the chief executive of the city. The mayor shall be inaugurated and take the oath of office in accordance with sections 10904 (relating to offices to be held until qualification of successors) and 10905 (relating to oath of office, violation of oath and penalty) on the first Monday of January after the regular municipal election. If the first Monday is a legal holiday, the mayor shall be inaugurated and take the oath the first day after that day or as soon after that day as possible.