Optimum opportunistic maintenance schedule over variable horizons considering multi-stage degradation and dynamic strategy

•An effective opportunistic model arranges multi-level maintenance for multi-component systems.•A reliability model evaluates complex degradation processes concerning imperfect maintenance.•Embedded dynamic strategy coordinates the maintenance schedules on the system and components.•An adapted renewal theory accommodates the maintenance optimization for variable horizons.•Real case studies are carried out to prove the efficiency and generality of proposed models.