Doing my best,
“Anyone know more about this? or how this would work?”
Einstein used a thought experiment involving a speeding train to demonstrate that time is relative to the inertial frame of the observer.
Suppose there is a speeding train, and there is a man in the middle of this train. Another man is sitting at a platform outside of the train as it speeds past. Right as the middle of the train is passing the platform, the man on the platform sees lightning strike both ends of the train simultaneously. What does the man inside the train observe? As light from the lightning heads towards his eyes, the train is moving in the direction of one of the bolts, and away from the other. Thus, the light from the lightning strike at the front of the train has a shorter distance to travel to the eyes of the man in the train than the light from the strike in the back. So he’d say the strikes were not simultaneous.