I was watching Battleship today, and they get the museum ship USS Missouri running in a few hours (yes I know this is stupid), but they light the boilers and get enough steam to sail during this time.
Surely the amount of water necessary to power a vessel like this would require hours upon hours of time to heat up and generate enough steam.
As a side question, did blockade ships in the US Civil War stay under steam 24 hours a day (in case they had to chase down a blockade runner)? That must have cost a tremendous amount of coal!
My question is simple...how long?
I don't think it would take as much time as you think. 600 PSI/850 degree Babcock and Wilcox boilers (the Iowa class used 8 of them, but they were common across the fleet) could go from a "cold" condition to ready to answer bells in about an hour or so under "emergency" conditions. A "normal" warmup (limiting the heat-up rate to prevent thermal stresses to the piping) could take four hours or so.
Most steam-powered vessels aren't kept in a "cold" condition; unless work on the steam system is needed, they're kept in a "hot standby"; the steam stop is shut and the steam in the piping is bled off. Even if one was stoking the boiler, it wouldn't take as much fuel as steaming would; heat is only being lost to the atmosphere rather than being used to power engines.