Most generally hair growth is 1\2 inch every month. So, the cutoff threshold for thc would be one small smoking session per month( 1 small joint, small bowl, or small edible). That's how you get three smoking sessions in 90 days and 1 1\2 inches of hair. That being said... If your head is shaved they will most likely take it from your armpit and if your armpit hair is 1-1 1\2 inches in length you should be fine.