Compared with electricity, hydrogen is easier to store and can play an important role in the high renewable energy integration. Under the background, this paper focuses on the influence of hydrogen demand (flexible hydrogen demand) at different time scales on the optimization of regional integrated energy systems. Firstly, the uncertainty of renewable energy output, demand-side response and flexible hydrogen demand are considered in the modeling of regional integrated energy systems. Then, the impact of hydrogen demand on the optimal dispatch of regional integrated energy systems is studied for different time scales with different photovoltaic penetration levels based on the hourly annual electricity load demand and photovoltaic output data. Finally, a simulation is included for verification with the goal of minimizing the annual operating cost of the system. It is shown that the system economy gradually improves as the time scale of hydrogen demand increases (the storage capacity of the terminal gradually increases) especially for area of the equipment operation, transaction with the upper-level grid, and demand-side response.