This doesn't really work, unless you wait until the trip is already more or less over, and you're just dealing with the lingering trippiness say, 7+ hrs after dropping it. In that case, assuming you have no benzo tolerance, .5mg, maybe 1mg might be appropriate, if you frequently take benzos, you'd need a higher dose. If you take it earlier, you'll just be high on xanax while tripping (resulting in a much shallower trip - can be fun sometimes) - I've taken xanax and other benzos with psychedelics, and until you're well into the comedown, they won't let you sleep.
Trip another time, if you don't have long enough to devote to tripping tonight.