Those buttons are used all the time at every terminal station where the train sits for a few minutes.
The doors closing early is just helping raise GO’s on time performance, if they closed them right on departure time that means by the time the train is moving it’s already almost a minute late, this prevents that. You might’ve noticed already that most CSA’s close the doors 30 seconds before scheduled departure, not many people have been complaining about that, so I don’t see how an extra 30 seconds will be such a big deal.