Pisa is a very nice little town, which can be visited in just a few hours (1 day max). Our plane arrived there at 5 PM, we've checked-in in our B&B, and from 6 PM still had plenty of time to see the Pisa Tower, and some interesting parts of the city. A week later, before plane, we also decided to spent the evening in Pisa, and it was really cool.
Insider Tip:If You want to eat something good, there are two nice, neighboring restaurants near the tower on Via Cardinale Maffi Pietro. We've eaten in both of them. From the closer one we went hungry... The other one was perfect. It's the one that is a little bit further from the tower. Just sit there, relax, and eat something from the tourist menu :) They have a very tasty pizza (in fact it's a simple margherita, but for 1-2 Euro they can make it better with parmigiano ham or sth else). Best regards, Bartosz :)