THE HALF LIFE is 16.3 hours, so after 16.3 hours you'd have .25 in you, .125 after 16.3h more, etc.....but these are averages......you need to know the sensitivity of the test. also, you may eliminate faster or slower based on many factors.
its a complicated question.....i used to take 3 mg klonopin a day and it did not show up on a standard urinalysis, which was extremely strange, given klonopins long half life.....they used a more detailed test, whatever that was, and it showed.
bottom line, it depends, but id guess after 6 half lives, or 96 hours, youre safe.