The effect of the local is immediate, sometimes they go too deep for a local to work well which is the reason for the conscious sedation. There is a huge YMMV on this one. I went a few years without the sedation until I got a new pain doc that used sedation over local at that time I wished that I met him a few years earlier. Of course you can't eat or drink 8 hours before or drive home but its a hell of a lot more comfortable.