I have seen research that indicates that it takes up to 2 years to lose your tolerance to benzos and get to where they work again at the same dose. Also, I know many pdocs and medical researchers say that after coming off a benzo wait two years to try going back on one. Tolerance is a enduring thing with benzos.
But surely that assumes that one has taken it as a prescription on a daily basis? I have only ever taken diazepam on an as-and-when basis. The most consecutive days would not have exceeded 3 I would imagine - and only one dose for each of those days. Still, I am doing my best to cut them out as much as possible so I shouldn't be concerned, but is just nice to know that they would still be effective in an emergency situation.