Sue, the ship docks at 7am but it's going to be later before even the first person can leave the ship. After the ship docks, it has to go through whatever Italian Customs procedures all arriving ships go through. If all goes smoothly and quickly, they could start letting folks off the ship between 7:30-8am. Unless you roll all your luggage off the ship yourselves, you have to wait in line to disembark, then go claim your luggage, before leaving the ship terminal. You could be one of many people waiting to get off the ship, and be in a long line.
Considering the airlines now recommend that you arrive at the airport between 2 and 3 hours prior to an international flight, I don't think 10am is a good idea for your departing flight.
As an example, Royal Caribbean recommends booking flights no earlier than 11:30am when departing one of their ships in Venice.