Milan for two days or day trip to Cinque Terre?

If you want to see the Cinque, why not route yourself to the coast from Florence and spend one night. The next day take the train to Milano for your remaining 2 days. The distance from Milan to Cinque Terre is pretty far even by train. Good luck - the Cinque Terre is a beautiful area with extraordinary food, but so is all of Italy!!

If you’d rather see CT then do that from Florence
If you don’t want to stay over there are day trips offered from Florence as well that will likely be less expensive and definitely less time traveling

Milan probably doesn’t need 3 nights and if you drop the day trip to Lake Como then 2 is probably more than sufficient
Add the night to Florence for your CT day trip

You need to read more about the Cinque Terre, Milan and Italy. The Cinque Terre can be horrifically crowded or they can provide the hike of a lifetime. Much also depends on what time of year you are going. Few people would think that a short tour would be worth 7 hours of travel plus the tour fees.

Cinque Terre is fantastic, but it's a looong trip, even from Florence. If it were me, I'd leave it for the next trip and instead spend the night up (or two) on Lake Como. After Venice and Florence, you're going to want the break from the hustle and Varenna/Bellagio could be just the ticket for you.

7 hours on a bus? There’s no way I would spend that much of my limited vacation time. If you need ideas for what to do as day trips from your bases, here are a few ideas:

From Venice:
Padova, Vicenza, Verona, boat trip on the Brenta Canal

From Florence:
Tuscan countryside hill towns, Siena

While there is enough to do in Milan for two days, in my opinion, it pales beside the glories of the Lake district. You might consider staying over a night or two and exploring Lake Maggiore as well as Como. While different from the CT, not only is the scenery gorgeous; but there are other interesting aspects which are absent from the CT.

cpollady - Instead of combining Cinque Terre with Lake Como on those last 3 days in Milan as a day trip. Why not just include Lake Como with Lugano for a full day tour. Lugano and Como are less then 30 minutes away. That might work for you very well. Consider it.

If you don’t already have non refundable flights and hotels booked, you might want to make several changes. But, it’s based on what you want to see & do. First, I would fly into Venice instead of Milan - no reason to take the train to Venice if that’s where you’re beginning. Then, pick up a RS guidebook and read through all of the options for each of the towns you’re considering. Personally, i wouldn’t spend any days in Milan for a first or second trip to Italy, but your interests may be completely different. Reading the guidebook will uncover your priorities.

For day trips, we don’t go longer than 1 1/2 hours one way; otherwise, we’re using up valuable vacation time just for transportation. Look at the guidebook for Cinque Terre and determine if you want to stay overnight and make it the stop after Florence. Or, you might stay in Lucca after Florence, go see Cinque Terre as a reasonable day trip, see the leaning tower of Pisa, and just head to Milan or a hotel at Malpensa for your last night.