Well, I don't think so, but I'm not a cruiser and I love Venice.
If the ship docks at 14:00, when will the first folks off be heading down the gangplank?
If you are one of the first off the boat and it takes you about an hour to get you into the thick of things and you get your bearings quickly it will be 15:30.
You don't say when this cruise is. The English language Secret Itineraries Tour is at 9:55 and 11:35 only unless you pay extra and not there during July or August. The Secret Itineraries Tour is also available after 1 pm (until the closing time of Palace) with an additional payment of 31 euro per group purchasing at least 15 tickets.
Unless you organize it in advance I think that would be difficult to count on. The tour takes about 1 hour and 15 minutes and then you have access, without a guide, to the Doge’s Palace. So that sounds like all the rest of the afternoon to me.
Will you return to the boat for dinner? If so, will you go back into Venice after dinner?
Then they want you to be off the boat early the next morning. What's early? 5am? 9am? Breakfast? Then over to the train station to leave your luggage which will be x-rayed. Figure an hour for that. Your train out will be at 13:35 to Munich - 1 change? That's a Eurocity. How early will you want to board? And you have to retrieve your luggage in the station. An hour to 90 minutes incase there are delays getting your luggage out?
So that gives you around 3 hours that day in Venice to "get a good basic feel for the city". With a group of 5. Is that kids or adults?
I think that is tight. Just a round trip on the Grand Canal will take 60-90 minutes or more. A walk through the little lanes getting lost you won't have time for, nor any of the churches, nor any cicchetti, nor any of Dorsoduro nor Cannaregio. Do the kids or other adults in the group move quickly and not need lots of "stops"?
But it may work out really well for you and you may be quite different to me...
