all I know is I get random drug screenings at a methadone clinic going on 3 yrs now and I take either ativan or xanex which both have relatively low half lives { xanex's is a little longer than ativan's} but I only take 1 to 2 days off at the most before going in on my pick up days and I'v passed every time... I do have a very fast metabolism though. I would stay away from klonopin though, it has an unusually long half life among the benzodiazipam family which most people would'nt assume, since it is on the weaker side as far as benzos go. If you need to find out accurate half lives [ which is basically half the amount of time a drug metabolizes in... so in other words say the half life is 12 hrs... multiply that by 2... check out wikapedia for reliable info. But always waiting as long as u can, drinking pleanty of water and taking your meatabolizim into concideration is important. There is really no difinative answer for this question because every one's different and there are a lot of factors that effect how fast your body expels a drugs even down to simple things like your diet, if you take vitamins or supplements etc. So I'm just sharing my personal expierance with how I'v managed to pass my drug tests. I hope this was helpful to someone.