Need Northern Italy Itinerary Help

Hi Lisa, I don't see any major changes needed. If you do shift days around, keep in mind that museums can be closed on Mondays and if you're traveling by train, there's less options on Sundays. Depending on what you're wanting to see Sept. 24, the Monday closings might play into your plans.

Your trips from Ortisei to Venice and then on to the Cinque Terre are both rather long. You'll have one full day plus a few hours in Venice, which I fear will end with your not liking the city much, since you won't have time to spend much time away from the tourist-clogged top sights. I see nowhere you could steal an extra night, unfortunately. Personally, I'd drop one of the destinations to provide a bit more time, at least for Venice and Rome. 2-1/2 days is very short for Rome.

Given the places you want to go, the order you list looks to be as good as it gets.

Now for the unsolicited commentary. As nice as CT is, adding days to Rome and Venice and skipping CT this trip, may make for a better overall experience.
Yours is an aggressive itinerary, but I have seen less pleasant proposals put forth on this forum.

If this is your preferred style of travel, then go for it.

Thanks for everyone's feedback. My wife likes big cities and I like the mountains/hiking/small towns. This is our compromise and why I don't want to cut the CT and add days to Rome. I found Rome completely overwhelming the last time I was there, but my wife has never seen it. I am now working with a slightly modified itinerary that has 3 nights in each place except Venice. I know the Venice people will balk, but there isn't time to add more. I enjoyed it last time I was there but I remember thinking two nights was plenty. The only long travel day will be going from CT to Ortisei, but it's only one long day out of the trip. Last time I was in Europe I visited eight countries/16 cities in five weeks on my own, so this seems slightly more sedate.

9/13 Fly to Rome (overnight flight)
9/14 Rome (sleep in Rome)
9/15 Rome (sleep in Rome)
9/16 Rome (sleep in Rome)
9/17 To Florence/Siena (sleep in Florence or Siena)
9/18 Florence/Siena (sleep in Florence or Siena)
9/19 Volterra/San Gimignano day trip (sleep in Florence or Siena)
9/20 Leave early to Cinque Terre (sleep in Vernazza)
9/21 Cinque Terre (sleep in Vernazza)
9/22 Cinque Terre (sleep in Vernazza)
9/23 Leave early to Dolomites/Val Gardena (sleep in Ortisei)
9/24 Dolomites/Val Gardena (sleep in Ortisei)
9/25 Dolomites/Val Gardena (sleep in Ortisei)
9/26 Leave early to Venice (sleep in Venice)
9/27 Venice (sleep in Venice)
9/28 Fly home

Check transportation schedules carefully for the Ortisei-Venice leg. If you don't catch the 8:31 AM train out of Bolzano, the next good option doesn't depart until 11:31. There's an 8:36 AM departure, but it takes either 5 or 5-1/2 hours, depending on what connections you choose in Verona.