I would give a minimum to two days to every city, and would prefer 3-4.
And, during that time, you might want to consider day trips to smaller towns, outside of the big cities.
Plus, you have to allow for travel time between cities.
btw—Zurich, IMHO was not that exciting.

I would figure an average of 3 days per city. Assuming there’s some travel time involved, I’d plan 4 days for Paris and Rome, 3 for Madrid, Barcelona, Prague. At least 2 for Amsterdam.

I’d look at Bruges instead of or in addition to Brussels (1/2 day if it includes an evening is enough for Brussels). IMO, you don’t visit Switzerland to see cities. I’d skip Zurich in favor of almost anyplace alpine and small. I’d replace Pisa with Florence and visit Pisa as a day trip if you really want to see it.

I agree with Cil, spend time for 2days.

Ditto.

I’d plan on at least two days per place… plus a day for traveling n’ stuff. Even if you fly from place to place for the longer trips you still have to make it to the airport and check in… wait for the flight… catch a bus or metro back to the next city. All that takes up time.

I think your day by day breakdown is pretty good, but also it’s ok to remain flexible with your options. Keep your options open… maybe you’d like to stay an extra day or two at one of the stops? I’d also agree with Bruges as a cool place to go. I wanted to make it to Brussels on my last trip, but had such a good time in Bruges I never made it there.

go to Munich instead of Salzburg in my opinion, and then Interlaken instead of Zurich