If you do decide to deworm regularly it honestly can be done as often as you feel necessary.
Some people choose to do a fecal test regularly instead and only worm as needed.
IMO it comes down to what your rabbits lifestyle is like....
Are they exposed to other animals?
How often do they go outside?
What is their environment like, during what times of year?
Do you take them anywhere?
If youre looking to just deworm, then I like using "Fenbendazole", sorry dont know the dose off the top of my head, have the doses and paperwork back at home. Its pretty safe and has a fairly wide range of uses and doses depending on the parasite or issue in question.
But do remember, just because an animal is 100% indoors and doesnt get exposed to other animals, does NOT mean it is safe from parasites.