1) Yes, synthetic urine has a shelf life. Anywhere from 18-24 months. You can always test your synthetic batch with a validity test kit to see if the urine constituents (creatinine, pH, S/G, etc..) are within satisfactory ranges. Do a Google search for "drug adulteration test kits".


2) Niacin is an ancient myth. It does nothing to help pass a U/A.

3) A no-brainer - the more you toke, the more THC is in your system.

4) See #3


Each persons body is different. Therefore, cleanout times vary from user to user.
What you should do is pick up some home THC test kits and test yourself periodically so you'll have an idea how long it would take for you to finally test negative. For each testing session, be sure to use the first urination of the day.