Do you have plane tickets? Where are you flying in and out of?
Germany is a big country. All the other places you list are towns or cities but Germany is an entire country. Where did you have in mind?
What made you choose the places you did choose? Is there a common thread?
Each day of relocation takes a half to a whole day, including the disruption of upping sticks and getting familiar with a new place, to say nothing of the actual transportation time and confusion time.
Are you using trains or a car?
Regardless of the length of the trip, I would suggest, based on personal experience,
Rome, at least 4 nights, preferably at least 5
Florence, at least 3 nights
Venice, at least 3 or 4 nights
Interlaken, don't stay there, stay in the mountains nearby at least 3 nights, preferably 4 to be sure of seeing what you want
Lucerne, at least 2 nights
Zurich, skip it unless there is a reason you want to go there (why did you choose it?)
Paris, at least 5 nights
Amsterdam, at least 3 nights
Germany - how long is a piece of string? Where? I'd spend at least 3 nights in Munich, 4 nights in Berlin, 4 nights in Black Forest/Alsace, 2 nights Frankfurt, and you haven't hit any of the tourist areas yet.
So that's 28 nights, more than you have.
Of the places you list, what can you live without?