Usually, if
DCL books the room for you, you don't have to select a Port Arrival Time. That's about it.
Since the terminal doesn't open until 10:30, and it takes about a hour from MCO to port, 9:30 would get you there by that time.
You can arrive after your PAT with no problem. Arriving before your PAT, via DCL transfers, you will be allowed to enter the terminal, regardless of what time it is. BUT your boarding number that you get at check in is tied to your PAT.
PAT is the window that you plan to arrive at the port. But it's really a "no earlier than" time, not a hard window that you MUST arrive during.