On our VFR Tour last October, our group visited the Uffizi first thing in the morning. We were there for about 3 hours. Granted, we didn't see everything (we were with a local guide who focused on the art work on the top floor), but I felt we saw enough. After the Uffizi, we were on our own for the rest of the day until late afternoon when we had group tickets to the Accademia. In the interim, we visited the Bargello Museum (not to be missed in my opinion), had lunch (and gelato, of course), went back to the hotel to recharge, and then headed out to meet the group for the Accademia tour. I didn't feel that it was too much to see or cram into a day. And, to echo what Threadwear said, there's definingly a "waiting to get in situation" at the Accademia, even with timed-entry group tickets. I'm not sure why, though; maybe they need to adopt the policy of the Borghese in Rome...everyone gets 2 hours max.