Different people metabolize benzodiazepenes (Valium and its related drugs) at different rates. That range is probably a pretty good one. I'd be apt to lean toward the longer number rather than the shorter one. Depends on how many Valiums you typically take and how old you are and how much you weigh. How fast your metabolic rate is and how efficient your liver and kidneys are at filtering it out. How fast you clear it will vary from person to person.