Sailed out of Baltimore about 4 years ago - the end of October. My pictures of the Key bridge are daylight. I believe we left at 5 so it had to be less than an hour. BUT that is when they sailed out of Dundalk, so I would add another 30 - 60 minutes. It was late ehen we when over the Chespeake bay bridge/ Tunnel - around 10pm.
2 Royal Caribbean
1 American Hawaii
Holland America 1/15/11
Going out of Port of Baltimore is wonderful. Locust Point is well organized and friendly.
To answer your original question, it takes about 1/2 hour to go under the Key Bridge. It takes about 2 hours (possibly 1 1/2) to get to the Chesapeake Bay Bridge. It is between 10 pm and midnight when you get to the bridge in Virginia that is 1/2 underground and 1/2 over the water.
For 2008 and 2009 the Granduer alternates 5 night Bermuda cruises with a 9 night New England cruse to Portland and Bar Harbor Maine, Halifax, St. Johns, and Boston. It also does a 9 night Caribbean cruise to San Juan, St. Thomas, Samana, and Labada. All are wonderful cruises.
We've been fortunate to take all three cruises. We love this ship and love going out of this port.
My wife and I sailed out of Baltimore last fall. The only other cruise I had been on was out of Miami many, many years ago. The Baltimore port was a very nice experience. It was easy to find, parking was great and embarkation was a breeze. We sailed at around 4PM and reached the bridge quickly. Everyone cheered when we cleared it as from our vantage point it looked as though it would be close(even though I'm sure it wasn't.)
The first night, I remember waking up around midnight to bright lights on our stateroom ceiling. I looked out our window and there was another ship returning to port not more than fifty yards away from us. I guess the shipping lane must be pretty narrow until open sea is reached and the ships that pass eachother have to be pretty close.