we have 1 free day in the midst of the tours we are taking (we are doing tours of Sistine/Vatican/coliseum/pantheon/Spanish steps/trevi fountain) and wanted to know if a day trip to Tuscany is feasible or it's too far?
Tuscany is an area. Florence is in Tuscany along with a dozen other cities. Where do you want to go? Personally I won't do because you will spend a lot of time on a train. Save it for another trip when you can take time to enjoy it.
Did you see the responses to your previous post?
https://community.ricksteves.com/travel-forum/italy/tuscany-7b5d9b65-dfe7-40e6-8c27-c5e798ef843d
If you want a day trip, go to Orvieto. It is a little over an hour by train. Quiet, charming town.