Cranberry is a mild diuretic and may provide some help in speeding the elimination of THC metabolites from your system. I wouldn’t rely on four pills the day before the test to get you a pass. The large amount of water would have much more of an effect, but simply drinking large amounts of water usually results in a “negative dilute” condition. The other factors in our dilution protocol help to make your dilute urine appear to be less dilute.
The only way to know when you’re clean enough to pass a test is to test yourself at home. You can get THC tests at drugstores for $15 - $20 each. You can get them in batches of 10 from sellers on eBay for $2 each. If you pass a home test with the first part of the first pee of the day, you’re home free.