Hi, It really depends, as everyone's biochemistry is unique. Typically, CBD oil taken consistently has a cumulative effect--best results occur in 2-3 months. A few experts have responded to Qs about sciatica: Dr. Edmunds recommends a holistic approach that includes a range of therapies from exercise and massage to acupuncture and cannabis (linked below). Dr. Persaud mentions that everyone responds differently and recommends you consult with your doctor on a proper course of treatment: https://www.hellomd.com/answers/59fb869f5aae0c0ac5a55481/what-do-you-recommend-for-chronic-extreme-sciatica-pain-that-is-not-psychoactive.
First of all, 'sciatica' can be caused by many conditions, some requiring intervention to prevent permanent loss of function. If you haven't been evaluated by a physician and scanned to find the source of your pain that should be the first priority. Cannabis can be helpful for reducing the discomfort of chronic pain. Many patients with chronic pain report the best results when using "whole plant" preparations that take advantage of the complementary action of all the cannabinoids, sometimes called the "entourage effect." Chronic pain creates emotional and mental effects that are also treated holistically with cannabis. I suggest checking out this simple article on this website to help get an idea of how cannabis may be helpful. I suggest beginning with small doses of preparations with generous amounts of CBD, perhaps a 1:1 CBD:THC ratio, and increasing dose and varying the ratio to find what seems most helpful.