The half life of the levonorgestrel dose is somewhere between 25 and 35 hours, but I suspect that you're asking one of two other questions.hat really depends on how many milligrams each capsule is and how often you take them. The average is 15-30 days or up to 90 days(heavy use every day) for a urine test. But o … nly 12-78 hours for a mouth swab(depending in how young/healthy you are.). Chrishan Silva.