You would certainly have time to do some stuff. Note that when you leave the baggage area, on your right is a machine where you can get a free transportation ticket for 80 min. You could either take the train into the town center (5 min) which is in the underground mall to your left as you exit the airport, or, also to your left is the #10 bus which does the same thing.
Once you are in the town center (Gare Cornavin) there are shops and restaurants all around, and you can easily walk down to Lake Geneva. You could also take the bus to near John Calvin's church, climb it's bell tower for a great view, or rent a free bike (www.geneveroule.ch).