hey hey dani
if that's what you want go for it. leave early morning, follow roberto's directions for train.
anything, special you want to see or do in cinque terre? get it done, watch your time getting to pisa and whatever you want to do, you could even go into the small town and have dinner and see what everyone doesn't want you to do.
buy roundtrip train tickets firenze (florence) to CT to pisa to firenze. make sure to activate/stamp ticket before boarding train.
opapisa.it
site to buy tickets to tower, you will need to buy with date and time online. get before flying to italy.
go have fun and enjoy. my first trip to italy was to rome and i wanted to ride a fast train, people said you don't have time, WHAT???
i'll go by myself, friend went and we went to naples LOL, best day trip while in rome, it was crazy & insane, cops in and out of their tanks with guns, rifles, uzis in plazas and street corners, walked back alleys to shop, eat pizza and desserts, talk with our hands to all the friendly people we met, had wine and chacuterie at outside table. back to train station laughing so much, happy to have a toilet on board.
aloha