Chewing of cage

Yesterday I got a 8 week old bunny.
He wants to be out of his cage all the time, usually he is out for 3 hours in the morning. Then i leave for work only 5 minutes after he is in his cage he starts chewing the bars. I don't have a fence yet so i can't leave him out of his cage while I'm gone. How can i minimize this behavior/will it reduce over time?

Try giving him something else to chew like bark from a willow tree; hopefully this will keep him occupied.

It's only been a day, give him time to adjust - he's a baby and he just got put into a foreign place by a complete stranger. I really wouldn't add anything to his diet right now, he's young and in a stressful situation already and you really don't want an upset tummy on an 8 weeks old. 3 hours a day is not enough time outside of his cage, though. You'll have to bunny proof a room quickly or to buy a play pen to link to the cage where you'll be able to put cardboard boxes and a little house or something so he can occupy himself.