Vyta has a couple spots at Santa Maria Novella Station in Florence. One is located in the main station just in front the platform barrier. The second is down the escalator in the shopping mall under the station, just a couple minutes walk from the platforms. There is more comfortable seating there. Opening hours seem to be around 8am to 8pm daily.
We grabbed a table at this Vyta, had a round of their illy brand coffee which is just fine and a couple of pastries while waiting an outbound train out of Florence recently. Service was ok, prices fine. Seats were quite useful if you don't want to stand with the crowds of awaiting train passengers up top. Would stop here again before outbound train trip again on that basis.