The 2019 Regulations on the Selection and Appointment of Party and Government Leading Cadres set minimum years. To be promoted to a county or division post, a cadre needs at least five years of work and two years at the grassroots. A deputy must serve two years before becoming the head. The head of a lower unit must serve three years before becoming a deputy one level up.
Promotion outside these rules is called poge tiba, breaking the frame. Article 9 says it must be strictly controlled. No one may break the frame on years of service twice in a row, or skip two levels at once.