I guess it would depend on how fast you walk but it would be between five and six minutes. You take the elevator to the lobby level and then need to walk into the main Venetian lobby and then down the corridor to the casino floor.
The main Venetian tower is certainly a shorter walk to the casino.
We have stayed in both towers many times and really enjoy the Venetian as our home away from home but the Venezia Tower is nothing special for us.