Pretty good so far!
Let me clarify come things though-
Distance from ship to bus- Yes, it depends on where the Celebrity docks, but the port entrance is a walk from all the docks. You'll go to one main port entrance (it will be where all the taxis are waiting) Look for the bus station outside of that.
Which Metro train do you take- There is only one. The "green" line stops at the port so when you get to the train (more like a subway) you can only go into Athens.
Which stop? To get closest to the Arcopolis you want to get out at the "AKropolis" station But to get to that one you will need to change from the green line to the blue line and then the red line. See this
map. So you take the green line to the Monastriraki station get out, follow the signs to the blue line get on and go to the Syntagma station, get out and go to the red line to the Akropolis station. Leave the subway and you will be across the street from the main entrance. (You could just get off at Thissio but you will be on the back side of the Acropolis site and have to walk a long way to get there. Its easier to do the transfers)
What else would you like to see? Well when you are done with the Acropolis , get back on the subway and go to Syntagma and get out.. you will be where the changing of the guards is. If you walk back about 1/2 towards the Acropolis you will be in the Plaka area (have a nice lunch)
Schedule- I'm not sure you have to worry so much about a train schedule. The subways run fairly regularly. Just time your trip in (from the time you get off the ship) to determine how much time to leave to get back. I would add 45 mins to that time as "buffer" IN case you end up having to walk back to the ship from the train station or something .... Print out the train map and then google on Athens maps, some will transpose the metro lines on the city map and you can plan out where you want to go.
One last comment. Be aware of your surroundings on the green line. It is known for pickpockets and baggage thieves. They will wait until the doors almost close, grab your bag and jump off the train....etc...
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013