It isn't mandatory. I didn't really feel the effects of it until just after my procedure because they gave it to me a mere 2 minutes before the procedure so, it didn't get enough time to work its magic before the doc took me in to perform the surgery. I was groggy after the procedure which, along with the valium, I think had a lot to do with the fear, anxiety and stress I went through for weeks before the procedure. It was all over so, I could finally relax and my underlying tiredness really took over. That was good though since they tell you to go home and take a nap right afterwards to sleep off the post-op grainy and slightly stingy discomfort that you may feel as the numbing drops wear off. If you sleep for a couple hours, you will not feel any of that. In fact, I don't even know if I had any of that since I did sleep for about 2 hours post-op. So, do that. The valium will help in that instance if you want to hold off taking it until after the procedure. I don't know how long the effects of the valium lasted. I don't think it is too long.