It is possible or even likely that your ship will dock at the mainland port of Marghara, not at the Venice dock. That is where they have been going this summer, from reports I have read.
https://www.cnn.com/travel/article/venice-cruise-ship-ban-government/index.html
https://www.cruisemapper.com/ports/venice-port-79
So if you might want to do an overnight trip somewhere else, the time to do that would be straight from the ship after the cruise—-head to the train station at Mestre. Then return to Venice for the rest of the time before your flight home (assuming you are departing from the Venice airport). Book the return train to Venice Santa Lucia. Walking out of that train station to see the Grand Canal in front of you still gives me chills (in a good way).
I have been to most of the places mentioned (all but Vicenza) and they are all worth a visit, but Padua is so close to Venice it makes a better daytrip. Ravenna is wonderful—-a nice welcoming moderately-priced town, and the mosaics are stunningly beautiful. The train journey is 2.5 to 3 hours each way.
We went to Bassano di Grappa from Venice to see the famous Palladio bridge, and really enjoyed our short time in the city, but mainly because of our interest in all things Palladian.
Verona would be a good choice, or Verona plus Lago di Garda, a 15-minute train ride from Verona (to Pescadero del Garda). Take a boat up the lake to Malcescine—-it should be lovely there in June. There are nice beachfront hotels, a charming co=bled old town, a ruined castle, and a cablecar to ride to the top of Monte Baldo for hiking or sightseeing.
https://www.visitmalcesine.com/en
Or simply return to Venice. “Is five days too much time in Venice?” It depends on you. We have spent as long as a full month there, and then returned another time for a week. But we never go there in summer. For a first-time visitor, in summer, I would recommend exploring at least one other town close by. You will likely find the lodging cheaper and the food better. . . .