I too have allergies and ashtma and IBS. I am on day 16. For me the ideal would be 30 days or more. After two weeks of being able to breath freely and with my mouth closed I am not in a hurry to go back.
After the Master-Cleanse eat sparingly and mostly veggetables, beware of corn and potatoes. Try to cut out all meats and refined oils. Since your metabolism will slow down while on the cleanse I think it is very important to eat smaller portions than normal for a long while. It is also important to exercise. Even an hour walk every day is good.