Hi ,
At this time, there isn't a way to directly control camera speed for videos in Twinmotion directly. The speed is determined by the distance the camera has to travel and the length of the video part. The idea behind this was to simplify the UI as much as possible, automating this particular setting to make it quicker and easier to produce a video, although this does make it harder to use more advanced techniques.
I recommend submitting feedback on our roadmap here for an UI improvement you would like to see in future updates around this so the team can see if it is feasible.
Best,
Raghib