How long would you need for Uffizi and Accademia? My husband and I do not know much about art but want to see as much as we can.
The Uffizi is enormous, don't feel like you have to see/love all of it. I would estimate a couple of hours, maybe more. You might wanr to consider a tour or audioguide. The Accademia is reasonably small but you could easily spend one or two hours there, especially if you go upstairs to the picture galleries (I think it's worth it). On the same street as the Accademia is the Museum of San Marco, a former convent that has frescoes painted by Fra Angelico in the public areas and also in each of the rooms shere the friars used to live. It doesn't get that many visitors and you may enjoy having some great art almost to yourselves. About an hour for San Marco. If you can arrange your time over two days, I would start at San Marco, then the Accademia, then the next day go to the Uffizi (it covers the greatest time span).
The Accademia you can do in an hour. I've never understood the unique appeal of David, but David (and M's slaves/captives in the same gallery) are all most ever see. You could add another hour if you enjoy International Gothic panel paintings (a wonderful collection, upstairs), or the musical instrument collection, or the icons on the stairway, etc. For the Uffizi, most probably only survive 2-3 hours in an art museum, but days/weeks could be spent with that collection. Since you say you don't know much about art, I'd strongly suggest considering a high quality tour; the Uffizi is an amazing collection in which to learn if you'd like to know more about art. I've taken Context Florence's tour of the Uffizi (after having visited on my own a few times) and learned so much. The groups are limited to 6 people, which really enhances your ability to discuss the art with the guide. And the guides mostly have degrees in art history, and are consistently interesting.