yes, you have enough time to clean out naturally. there is no set amount to drink...just drink water, cranberry juice or even beer until you can drink no more...then drink more as time is short here. i found diuretics help immensly too. i used "aqua ban" but any otc diuretic works. you also say you don't exercise...it would be wise to begin. do whatever it takes to raise your metabolism and work up a sweat as much as you can stand. the day of the test take creatine or vitamin b2 to add gravity back to your urine along with color...or 3-4 one-a-day vitamins will do the same...it all helps.

good luck