They say you should need one month for each year that you have been ill but I would personnaly say at least 6 months, the first 3 being as strict as possible!!
I am on my 9th month now and personally plan to continue indefinitely. My plan is to not eat refined products - white flour, pasta, rice ec, no sugar, no wheat, no caffiene and minimum alcohol ongoing!! I feel so much heathier for it and have never felt 'totally' cured although 100 times better than I did!!!
I have relaxed my diet very slightly over time and have the odd alcoholic drink - gin and diet tonic, vodka and soda water and the very occasional small glass of dry wine - no more than once per week. Up to 2 pieces of low Sugar fruit per day - papaya, grapfruit, cooking apple, cranberries, blueberries, rhubard. Small portions of non-wheat, non refined carbs - sweet potato, quinoa, rice pasta, brown rice. Some low Sugar dairy - cottage cheese, live yoghurt.
Also plan to try and reduce some of my supplements and just take high probiotics and high vitamins supplement with low rotated antifungals!