Since it is not time-dependent, you don't have to calculate in advance when you'll probably arrive and then set up an unreliable alarm. Up to now I had always done it this way and always had to add a lot of Buffer (it could be that the train is too early this time - which happens more often than you think). But most of the time the trains are too late and are delayed and then the alarm goes off much too early and you always set new alarm times again and this is totally crazy and it just works badly the old way.
