The important thing to remember is that the timetable is written in military time instead of AM and PM. So train 123 leaves Jax for Ft Pierce at 18:00 hours or 6:00 PM to the rest of us. Because 18:00 - 12:00 = 6:00 PM. It arrives the following day in Ft Pierce at 11:00 AM. Actually earlier than that because it says the train must be available to consignees to pick up their containers. From 00:00 to 12:00 is AM. From 12:00 to 24:00 (or midnight) is PM.
I am fairly certain that "destination availability" means the time that a container is available to be picked up by the consignee. The railroad has to get the train in the yard and get the containers off, then the consignee can send a driver to the yard to pick up his container after the time shown on the timetable.