What is specified is the actual departure time of the train. Before that it has to be decided to start closing the doors, the doors must be closing, the secure

What is specified is the actual departure time of the train. Before that it has to be decided to start closing the doors, the doors must be closing, the secure closure must be determined by the train leader and the train leader has to order the train driver to start driving. How long that takes depends on the train. For short-distance trains it's ~15seconds for long-distance ~1minute.