Bus trip: Florence--> Siena--> San Gimignano--> Florence, need guidance

I hereby declare the city of Poggibonsi as the most misspelled city in the world by English speaking people.

Timetables are here:
http://www.tiemmespa.it/index.php/Viaggia-con-noi/Orari-e-linee/Siena/Extraurbano
Select applicable tables
130-A: SIENA > POGGIBONSI > SAN GIMIGNANO
130-R: SAN GIMIGNANO > POGGIBONSI > SIENA
131O-A: SIENA >COLLE V.E. >POGGIBONSI >FLORENCE

A=Andata (going)
R=Ritorno (return)
O=Ordinaria (Ordinary, I.e. Not express)

Siena to SG requires no bus changes (bus 130 all the way)

SG to Florence requires one change:
Bus 130 from SG back to. Poggibonsi train station
Then at Poggibonsi train station you take the bus 131O to Florence
Note that from Poggibonsi you could also take a train to Florence.

You can also use this site for easy search
http://www.busfox.com/timetable/

No bus station in San Gimignano. The bus stops in a piazza at Porta San Giovanni.
https://maps.google.com/maps/place?ftid=0x132a3c4734198c85:0x69d165810f60c9f5&q=porta+san+giovanni+san+gimignano&hl=en&ui=maps_mini

As an alternative to Roberto's nice info, Grayline has a bus tour from Florence that includes both San Gimignano and Siena. Cost when we did this was 52Euro. I see on their website that it's now 55Euro. A bit more than you doing it yourself but it is an alternative. It does include a walking tour in Siena and covers the entrance cost to the large church there. In Firenze, Grayline operates as CAF Tours. http://www.caftours.com/excursion-to-siena-san-gimignano-and-chianti-landscapes.html

I appreciate what you're looking to do here, but with this plan, you will spend a lot of time either on buses or waiting for buses, and will probably end up seeing both San Gimignano and Siena during the mid-morning to late-afternoon time period, when both places are full of other day-trippers. I enjoyed both of them very much, but the best times in both are earlier in the morning, or in the late afternoon and evening, when the crowds are smaller and temperatures are likely lower. Especially Siena is magical in the evening, with the Campo and major public buildings illuminated. I would encourage you to give Siena more time late in the day. You might want to take a day to visit each town, maybe having dinner and spending the night in between in Siena.

Thanks for the replies. We have a room paid for in Florence so overnight in Siena isn't an option. I hate being a daytripper! And I really wanted to avoid coach buses completely...I know we could do one that'd get us to Pisa too, but all I want to do there is see the Tower. Once we start talking private drivers I think prices become prohibitive. IF I could find a driver just for the Siena-SG portion, we could stay late and still take the bus back to Florence, but I haven't even thought about that til just this second.

And mea culpa on the spelling, the irony is that I'm usually meticulous about spelling and grammar but typing remains a weakness :-).

Off to search the bus schedules!

If you intend to ride the public buses, it's fine. Just watch out for traveling on Sundays. The bus schedules in Tuscany on Sundays are quite limited.

I agree don't go on Sunday. I went to Siena from Florence on Saturday and spent the night. SIgnificantly less buses on Sunday... understandably but I did not check first. I would spend the whole day in Siena but that is just an opinion. Also concerning Pisa... we enjoyed seeing and climbing the tower, the Baptistery was great and we also liked the church. Easy walk from train to the Tower area and we enjoyed walking through the town.