The presentation and timing of external human-machine interfaces (eHMI) for autonomous vehicles were found to significantly influence pedestrians' crossing decisions. Therefore, understanding pedestrians' interpretations of autonomous vehicles' intentions is of great importance. A simulation model was constructed using Unity 3D, and 16 videos depicting approaching autonomous vehicles with varying presentations and timings of vehicle intentions were generated. These videos were presented to participants in a randomized order to gather data on their reaction times and crossing decisions in response to the different scenarios. The results show that in terms of presentation, prominent text colors, as opposed to neutral colors, tend to significantly impact pedestrians' crossing decisions. This effect notably reduces pedestrians' reaction times and assists in making more accurate and safer crossing decisions. Regarding the timing of presentation, it is observed that a closer activation distance positively influences pedestrians' crossing decisions when autonomous vehicles' speeds are between 35 ~ 40 km/h. The closer the activation distance, the more positive the impact on pedestrians' crossing decisions.