No one can tell you how fast the thc metabolites that are tested for will remain in the body. Everyone is different. But if I were you, and that were my scenario, I'd def. sub with Quick Fix or something. Have you tried taking some over the counter drug tests using your first void (the one that will have the highest concentration of metabolites)?

Anyways. Sub is the way to go with doubts like yours. Just make sure you practice your temp to get it within the 90-100 range.