At the end of my trip (May 15) I will need to get from the B&B I am staying at in Venice located in Mestre to the airport for a flight departing at 6:45 AM, which means I need to be there at about 4 AM. Is it possible to get some sort of transport at that hour or am I better to just go out to the airport at about 11 PM and plan to cat nap in the airport until it is time for my flight?
The first ATVO bus departs Mestre at 5:20am. It's a 17 minute ride. Arriving at 05:40am may be a little tight. As for arriving at 4am, I'm not sure the airport is even open at that time. One option is to ask your hotel if they can have a taxi waiting at 4:30 or 5:00 to take you to the airport. The expense shouldn't be too bad. Finally, you have two other choices. 1) stay in a hotel near the airport. The Courtyard by Marriott has one within walking distance. Another is the Titian Inn & Hotel Residence. They have a shuttle. 2) sleep in the airport. See www.sleepinginairports.com. I believe its common to do this at Marco Polo. They do lock you into the terminal for the night. I don't know what time they lock the doors.
At that time, that is a domestic flight so 5 to 5:15 or even 5:30 should be more than adequate time.