Travel time between Venice's Zattere stop and Santa Lucia railway station?

Unless you have a reason to be in Florence early, I wouldn't be too concerned about the time as there are numerous high speed trains every day on that route. If you arrive too early, your next hotel room may not have been serviced yet.

You can check the schedules for the Vaporetti on this site - http://actv.avmspa.it/en/content/orari-servizio-di-navigazione-0 . I believe Line 5.2 is the one you'll need. According to the schedule, the shortest travel time from Zattere to Ferrovia (Santa Maria Lucia) is about 19 minutes.

Don't forget to validate your Vaporetto tickets on the electronic reader, or you'll face hefty fines!

The precise schedule depends on when you will be in Venice. For summer, the 6:56 #5.2 at Zattere arrives at Ferrovia at 7:15 AM. The waterbus before that is: 6:33 Zattere - 6:50 Ferrovia. Figure 17-20 minutes.

The first #6 boat arrives at Zattere at 7:02 AM. Ten minutes later, at 7:12, it arrives at Piazzale Roma. But you'd have to walk/run to Ferrovia.

If you want to go even earlier, you can, the number 1 in the Grand Canal has a night service - all night. A quick walk between Zattere and Accademia and the boat stops right there. Straight shot on the Grand Canal - and the views early in the morning are great.

The first daytime number 1 is at 5:03, every 20 minutes until 6:37 then every 12. It takes 28 minutes to Ferrovia. The faster number 2 up the Grand Canal doesn't start until 9 am.

You could also do the number 2 from Zattere through the Giudecca Canal at about 5:50, 6:10, 6:29, and every 13 minutes after that. Travel time 27 minutes.

My choice would be the number 1 from the short walk to Accademia.

Thank you all for the helpful advice and for the vaparetto schedules site!