Need some help planning our day in Fussen. We'll arrive by train Sat. night and pre-book early tours of the 2 castles. I've read lots of postings but can't figure out how long the tours of each castle are! I know to add time to take shuttle bus to Neuschwanstein. Also, if we have extra time before taking train back to Munich on Sunday, is the town of Fussen itself nice to walk around in? Thanks for your help.

The town of Fuessen is indeed nice to walk around in, it would be a pity to miss it. Check their page for more:
http://www.tourismus-fuessen.de/244.0.html

According to the castle website, tours last about 35 minutes.

In addition to adding time outside of the actual tour to get from town up to Neuschwanstein, you should also add at least another half hour or more to walk up from the castle to the Marienbrucke.

We were just in Fussen and the castles in last month. When you book your tickets they book you at Hohenschwangau first and then 2 hours later you have your entrance at Neuschwanstein. So, for example Hohen. would be at 9:15am and then Neu. at 11:15am. Each guided tour is about 30-35 min. We arrived about 30 min. early for our tour of Hohen. which gave us plenty of time to walk around the entry area and take pictures.

After that tour we had plenty of time to take the bus up to Mary's Bridge, enjoy the view and take pictures and then walk down to the castle and take pictures of the grounds. If you walk up instead of taking the bus or carriage ride, you may want to wait until after your tour to go up to Mary's Bridge.

The town of Fussen is very charming and worth an hour or so of wandering - it is not very big.

FYI Marienbrucke and Mary's Bridge are the same thing.

I really wouldn't bother with the tour of Neuschwanstein. It was never used, and the inside has just been completed for tourists. It's no more real than the castle at Disneyland on the inside.

Hohenschwangau on the other hand is a castle with real history. I would tour that, then walk to Marienbruecke to get some good pictures of Neuschwanstein, then walk to Neuschwanstein itself from there, have a look at the outside, then walk back down to the car park.