The deflagration of oil mist in closed chambers often causes severe ship fire accidents. Based on a self-built visual oil mist deflagration experiment platform, this research analyzed the effect of the spray time on the oil mist deflagration characteristics and focused on the flame propagation process, velocity, gas temperature, and overpressure in a closed chamber. The results show that with increasing spray time, the flame propagation velocity, gas temperature and deflagration overpressure increased. However, with the continuous increase in spray time, the deflagration characteristics of oil mist decreased. When the spray continued for 35 s, the peak overpressure was measured to be approximately 1.655 MPa. When the spray time extended to 95 s, the peak overpressure decreased by approximately 31.2% relative to the value at 35 s because the increase in spray time contributed to a more stable spray state and a larger diffusion range. Concurrently, the evaporation of liquid droplets increased of the kerosene vapor content. These factors contribute to a more intense oil mist deflagration. However, continuous increase in spray time results in an excessive accumulation of fuel, which makes an insufficient reaction and a significant reduction in deflagration characteristics. Oil mist deflagration process can be divided into four stages: deflagration, turbulent combustion, stretching and self-extinguishing. The high-temperature and high-pressure range of oil mist deflagration concentrate near the deflagration center, approximately 100 cm from left wall of the chamber.