From experience the zone lets you in after 30 sec at most or so. Calling the aetheryte first gives everyone that bit of time to get in and barely extends the train more than a few minutes or so.

Either way, they got impatient and stopped calling aetherytes first on Light DC. I'm not sure why you'd take the time to scout a train, announce it on all your linkshells and share it with the community, then not let half of them in, but train conductor sets the rules so I'm not complaining.