msteacher

Add another day(or two) to Nice if you are able, especially if you want to see the surrounding area. However, at this time of year, it may be quite pricey.

janisj

Don't think of it as 3 'extra' days - they are just days you can use anywhere. That doesn't mean you have to ADD more places. IMO you definitely need at least one more day in Madrid. You basically have 1.5 days there and you will likely be jetlagged when you arrive so don't count on doing much of anything the first day.

If you want to see Nice and the area, then you'll want to add at least one day there. As it is you will only have 1.5 days so another day or 2 would be good.

So that leaves you 1 'extra' day (or none if you add two to Nice) which I'd add to Rome since it is a massive city w/ lots to see.

You definitely don't have time for Greece.