Coming in to Milan, I have an unexpected (and unplanned-for) half day to spend. I arrive from St. Moritz at 12:50pm on day 45 (Oct. 31st), then spend the rest of the day and night in Milan, then take the 8:05am to 10:28am train the next morning into Venice on day 46 (Nov 1). Wonder what Halloween in Milan is like?
Things to do in Milan after lunch: the Piazza Duomo and the giant cathedral, the Galleria Vittorio Emanuele II, the Sforza Castle, the La Scala opera house, da Vinci's "The Last Supper" in the churce of Santa Maria delle Grazie (for which I need a reservation), and the da Vinci Museum. There doesn't seem to be too much else here to warrant an extra day, so in the morning it's off to Venice. There are trains leaving Milan for Venice every half hour, so let's say I take the 9:05am which gets into Venice (St. Lucia) at 11:40am.
It looks like I can spend two full days (or rather, the 1-1/2 that I'll have) on just two things: the Grand Canal and the Piazza San Marco. The vaporetto that cruises the Grand Canal only takes about 35 minutes end to end, but there are 16 stops along the way and it's a hop-on-hop-off ride so I could visit the sights along the banks. And the Fodor's book says "it takes a full day to take in everything on the piazza thoroughly", including the Basilica di San Marco, the Palazzo Ducale, and the various churches and museums there.
Up next: Venice to Rome. The overnight train leaves late enough that I can get in a full day in Venice, then sleep on the way to Rome (11:30pm-6:56am), so that I'd only need one night in the Venice hotel.