If you have 6 hours or half a day to spend in Barnet, there are a few things you could do:
1. Visit the Old Courthouse Recreation Ground - this is a great spot for a picnic or to relax in the sunshine. It won't take long to visit, maybe an hour or two.
2. Explore Church Farmhouse Museum - this museum showcases the history of Barnet and it's free to visit. You could easily spend 2-3 hours here.
3. Go shopping at The Spires Shopping Center - this center has a variety of shops, eateries, and a cinema. You could spend 2-3 hours here, depending on how much shopping you want to do.
4. Have a drink or something to eat at The Black Horse Pub - this pub is located on the High Street and is known for its beer garden. It's a great spot to relax and people watch. You could spend an hour or two here.
Overall, there are plenty of things to do in Barnet that can be enjoyed in half a day. Consider choosing a few activities that interest you, and plan your time accordingly.