It is good to let your bunny be in their pen or in the garden for at least 4 hours. This is the recommended amount. The more their out the better! Just make sure they have access to water and some shade to cool them down in the hot weather. Here is my rabbit enjoying his daily time out in exploring garden.
If you have an indoor bunny, exercise is just as important. You can litter train them and putting some hay in their litter box is said to help. You will also need to bunny proof your house. If your bun has their own toys, they normally won't chew on house hold objects and mainly play with their toys.
Rabbits can also be trained. Have a look at this to learn how to train and care for your rabbit.
If there is any problems please contact me.
Here are some bunny products which I thought you may like. Have a look if your interested!