Venice to Tuscany Italy and Pompeii by train, how long?

so this will be my second time to Italy. I will be going in Feb to Venice. for 4 days. Last time I was there. I was there for 9 days and saw everything in 2 days in Rome. so I made it shorter, but now I wish I didn't because I want to see Florence and Tuscany, maybe even that Famous volcano pompeii.. I was thinking once I get there (4pm) get on a train, and hit I think Tuscany its the furthest right, how far of a train ride is that? I want to be in a hotel by 9 pm so I can sleep and start my 4 day adventure. I was thinking though of staying 2 days in Venice, and the other 2 days just have a crazy walking around sight seeing. I can sleep on the plane on the way home. so see several cities real quick in 2 days and the last 2 days in Venice. anybody have any info or negative feedback on this idea/plan?