The benefits may be noticed within days, but it is usual to undergo a course of supplementation taking the maximum dose daily over a 3 month period before easing off. As with most nutritional strategies to maintain health and to be inury free, the effects are subtle to the point of being impossible to measure. In answer to queries about benefits for connective tissue other than joints: the answer is "Yes". they are beneficial for tendons and even the skin, nails and hair.
Should a runner take them? My recommendation is to do so if you are over the age of 35, or have had a history of joint problems or injury, a family history of arthritis, if you are in a job that is stressful on your joints or if you are doing particularly heavy training or intense competition - or all of these!