We rook a private tour from the ship a few years ago - in one day we had a brief tour in Belfast, then drove to the Antrim coast, the rope bridge and the Giants Causeway with a few other stops.
If you are not sailing until 10 PM, you have plenty of time to do this, and even get back for dinner - our tour was probably something like 9 AM to 5 PM.
Here's a description of the day from my blog:
Northern Ireland 
