It took me about a month to achieve remission on Stelara and have maintained remission for over 6 years and counting.
All depends on the treatment......
I think I was into remission within 6 months of starting Remicade, and have been on it now for over 17 years with only little blips here and there.
I went into remission with diet, SCD, took around 6 weeks. Lasted until I cheated and drank a lot of alcohol one night (3 months). Based on my symptom score I am still in remission clinically but I do have inflammation. Remission via diet is very fragile and involves a lot of trial and error, unfortunately.