Large-scale integration of intermittent renewable energy, such as wind power generation, necessitates the requirement for sufficient flexibility resources in power systems. With the development of electricity market in China, it is a trend to encourage the investment of flexibility resources via market-based mechanisms. As a shorter market clearing timescale is helpful to more accurately reflect the fluctuations in renewable outputs and the demand for flexibility resources, there is a need to study the impacts of market clearing timescales on electricity market equilibrium outcomes, especially for flexibility resources. For this purpose, an equilibrium model for the day-ahead electricity market is developed based on the supply function equilibrium theory, taking considerations of different market clearing timescales and generators’ flexible regulation capability such as ramp rate. A nonlinear complementary approach is applied to solve the equilibrium problem. Numerical simulations show that when large-scale integration of intermittent renewable energy causes intense fluctuations in the net load, a shorter market clearing timescale can effectively reflect the market value of flexibility, thus increase the profits of flexibility resources.