Hi , I did contac Alamo FLL directly because I did need this information too. Here is the answer from Alamo:
Response (Brian) 03/18/2009 07:00 PM
Thank you for contacting Alamo Rent A Car.
The shuttle service to the port runs Noon- 3:00 PM. The service returning from the port runs 8:00 AM- 3:00 PM. Proceed to the shuttle area located on the 3rd floor for transportation to the Port.
Alamo Rent A Car
Hopefully this information is helpfull.