Nobody can realistically tell you how long it would take for you to test negative. Each persons body is different and there are too many variables to take into account. Only periodic testing with a THC test kit (using the first void of the day for each time) can give you that answer.

Drinking a bunch of water/cranberry juice in the days or weeks before a scheduled U/A is of no help. Read posts #8 and #13 of this thread to find out why:
http://boards.cannabis.com/drug-test...ur-system.html

...and read post #3 of this thread:
http://boards.cannabis.com/drug-test...ml#post2225714