[bdonlan]

The signal will often go green (or in the case of this line, ATC will show that the train is cleared to proceed) prior to the actual departure time. This is because the trains are not allowed to close their doors until they have a departure signal, so this has to happen well before the actual departure time. Depending on the station configuration and signalling technology the signal clearing may simply occur automatically once the line ahead is clear, so it's up to the train driver to ensure that they don't depart too early.