How often do you harvest compost piles?

In a worm box composting system, you do not change the bedding. You let the worms eat it. Bedding is typically a high carbon substrate such as damp newspaper or coconut husk.
You put food in the box and cover it with the damp bedding. If it stinks, or gets to wet or is overcome by gnats you may want to sift out the worms and start over.
Perhaps every 6 months you should divide out your worms, sift out the worm castings/poop (dark black fertilizer) and restart the system. DO NOT ADD BANANA PEELS to your worm bin. They always have flies in them which will contaminate your box and make it nasty. You may also want to avoid orange and Apple peels.

In the garden turn you compost into the garden at least once a year. Hint- grow tomatoes right next to your compost bin! RA, "the compost Guru"