Blizzard added a new Dragon Isles Dock Master with a timer in the latest Beta build that shows how much time’s left until the boat to the Dragon Isles arrives to Stormwind Harbor.
The boat to the Dragon Isles departs from the same place as the boat to Boralus Harbor. When it’s not there, you’ll see a timer above the Dock Master’s head that provides more information about when the boat arrives.
As far as I can tell, this does not currently work on the Horde side with the Dragon Isles zeppelin.
It would be cool to see this implemented for all boats and zeppelins in the game. The timer was discovered by MrGM on the Beta.