Florence - How long for Accademia?

If you don't get advance reservations, there's no telling how long the line will be to get into the building.
After you get into the building, you can walk around the David 4 times in 10 minutes.
There are 3 other Michelangelos there, if you take a look at those, you'll still be out of the building in 30 minutes.
But, again, no telling how long the line will be to get into the building, if you don't get advance reservations.

Closer to one hour than two, unless you also visit the upstairs painting galleries and the musical instruments collection..

I have raised sons, and I think yours will enjoy the music room at the Accademia. Reserve your tickets in advance! You just cannot go to Florence and not see "The Real David!" Also Michelangelo's "unfinished" works may fascinate them, as you can see the people 'stepping out' of the marble. He could see the people inside the big block of marble, and chiseled around them. They may also enjoy the Santa Croce Church which has the beautiful Crypts of Florence's most famous residents, and an adjacent leather factory.

Make sure you take them up to Palazzio Michelangelo - for sunset, where there's a huge 'fake David' and you can see all of Florence.

To see the Accademia, if you have advance reservations: 30 minutes.
To see the rest of Florence:
2 or 3 days.

Just wanted to agree with Donna. In addition to the Accademia, the Santo Croce church is a great place to visit. Many tombs of famous people there.

Also, the Piazza Michelangelo at dusk should not be missed. I took some of my favorite photos there one evening.

If my wife had her way, she'd still be there from three years ago.

Absolutely have a timed reservation. The lines are always horrendous. An hour is sufficient as David is pretty much it. You could spend time on the other art in the museum but there is better stuff elsewhere in Florence.

Let me put in a plug for the Brancacci Chapel -- this is a 15 minutes visit (they limit you to this if it is busy). It is amazing, your sons are likely to find it as interesting as any painting in Florence and it is where the Renaissance began.

An hour is plenty. Basically it's all about seeing The David, then there is a room next to that with other artwork. My daughter and I went a couple of years ago. It was to be the highlight of her trip. We bought tickets on line a few months before with skip the line. I'd suggest getting your tickets and taking the earliest reservation time you can. Seems the bus tour people hit the museum @10AM or so..it can get crowded in there, although they do limit the number of people going in each 15 min or so. Even the street the museum on gets overcrowded with people in both lines to get in.

If I was a 15 year old, I think climbing to the top of the bell tower or the Duomo would hold more interest than looking at sculptures for hours on end....

It is important to see the actual David, just like there is nothing like actually seeing the Tower of Pisa in person. Italy is the heart of art and culture. It's wonderful that you are exposing your sons to this.