In my view, Toledo needs at least a full day. In truth, if you're not big art fans, I thinks there's more to see in Toledo than in Madrid. And it's certainly a more atmospheric place.
In 2016 one could buy a wristband that provided entry to 6 or 7 secondary sights, most of which included tours offered once or twice a day. With less than a full day you would be scrambling to catch all the tours; it's not easy to do even over the course of a full day. I enjoyed the sights themselves (several known for their mudejar architecture) but the tours definitely added something. I don't know whether the tours will be offered on December 28, however.
The major sites (including the Cathedral, the El Greco Museum and the Santa Cruz Museum) are handled separately in terms of entry fees, but just walking the streets of the very large historic district would be many people's #1 attraction. I'm not sure which offer guided tours, but many major attractions have English-language audioguides these days.