There are different times for the different cruises:
http://www.wdwinfo.com/just_for_kids/piratecruise.htm
Here are the cruises:
Children ages 4-10 will be outfitted with a red/white striped pirate Mickey hat (or a bandana) and board their pirate ship (pontoon boat) under the supervision of the "pirate" crew. At each "port of call" a new treasure awaits. At the final stop, they can share their booty while enjoying lunch. At least two Cast Members accompany the children, which are all CPR certified. All participants must be potty trained. (No Pull-ups.)
Lunch is usually Peanut butter and jelly Uncrustables, Goldfish crackers, Rice Krispee Treat and fruit punch juice box
Albatross Treasure Cruise - Yacht and Beach Club Dock on Wednesday and Friday. The two hour voyage begins at 9:30am
Disney's Pirate Adventure - Grand Floridian Dock on Mondays, Wednesday, Thursday and Saturday. The two hour voyage begins at 9:30am
Island of the Caribbean Pirate Cruise - Caribbean Beach Resort Dock on Tuesdays. The two hour voyage begins at 9:30am.
Sassagoula River Adventure Cruise - Port Orleans Riverside Dock on Sunday, Tuesday and Thursday. The two hour voyage begins at 11:30am.
You can book this 180 days in advance by calling 407-WDW-DINE (407-939-3463)
The cost is $30.01 per child, a credit card is required at the time of booking, and parents must sign a waver upon arrival. Cancellation policy is 24 hours in advance and no show/ not canceled 24 hours in advance, is full charge.
**Young pirates must show up at the marina by 9:15am for the 9:30 voyage and 11:15am for the 11:30 voyage