We are arriving to the cruise port in August in morning. We have until 6p to spend time in Messina. What are your favorite sites?
I'm afraid I can't help you there, but I'd guess the cathedral is worth seeing. Messina doesn't figure on many tourists' Sicilian itineraries.
I think most cruise passengers head for Taormina; is there a reason you don't plan to do that?
Not the most interesting city in Sicily but a nice city to stroll around and try the granita and not only:
https://slowtravelitalyspain.blogspot.com/2019/04/east-coast-sicily-day-3-messina.html?m=1