Interaction designer running a global creative network called Mecenato. Airbnb hosting ran in conjuction with my partner, Dolores. We do it for the love of travel and travelers alike. We use all the funds from AirBnB for traveling.
This has been the first time, after several years of using Airbnb that we've had a problem with a guest and an were put in a very uncomfortable situation. There are several vaporetto (water taxi) lines that run between Lido and the train station, it's at the guests discretion to take the line that takes 35 minutes or the one that takes 1 hour. Taking into account the amount of people that visit Venice on a daily basis and the fact that it's public transportation, it's beyond our control to know if the trip is going to take longer or not. For those not willing to deal with public transport, there are water taxis available.
When making a reservation with us, guests are able to see our check-in and check-out time. We try to be flexible and accommodate guests needs but we are not a hotel and unfortunately we cannot always allow guests to leave their baggages after check-out time, especially if we have other guests coming, as it was the case this time. We believe that our check-out time is more than reasonable and would have given you enough time to visit the whole island.
I believe we were more than accommodating throughout their stay and we strongly suggest that in order to avoid such a bad moment for both you and the host next time, in case you will have specific check-out requirements, you mentioned it at the time of your reservation.