The video is showing part of that delay, but the blog entry is explicitly suggesting that the step start extending while the train is still in moving (at < 5 mph):
> This can be fixed in software. As seen in the timeline graphic, allowing the step to deploy and retract while the train is in motion would remove this wasted dwell time.
> This can be fixed in software. As seen in the timeline graphic, allowing the step to deploy and retract while the train is in motion would remove this wasted dwell time.