It wouldnt hurt to begin your creatine-loading right now.
How much creatine you would need would depend on what your "baseline" creatinine level was before loading - each persons baseline is different - and youre not going to know this without testing your creatinine with a validity test strip. You should have a few of these strips at hand anyway when doing dilution techniques, that way you can stay on top of your creatinine and well as the S/G. These strips are essentially the same colorimetric tests that will be used at the lab for your scheduled U/A. They are inexpensive and are found online by doing a Google search for "drug adulteration test kits"

How many hours prior to the test should I start diluting with gatorade?
Read the steps outlined in N2's thread here, beginning with Step #2.
http://boards.cannabis.com/drug-test...uidelines.html