I don't know for sure, I think it is different for everyone. But for me personally, I have been off all pharmaceuticals for over a year. (asacol,pentasa,nexium,prednisone,remicade)
I do have to smoke quite a lot now, atleast once a day. Whenever I feel symptoms coming on, I take my medication till I feel normal again.
Also I think the best way to get cannabis in your system with crohn's is either with a vaporizer or a tincture. I don't believe edibles work all that well because they may pass too fast.
Best of luck in your journey, I hope you find good health!