Having healthy dreads and maintaining their cleanliness is what I care about most. For locs that are just starting out, the majority of stylists and loc wearers advise every two to three weeks; as they mature, every four to six weeks. When there is a lot of new growth, that's really the only time most people retwist. Having said that, take the actions you deem necessary for your way of life. People who work out frequently and sweat easily will wash their hair more frequently and may like to maintain that neat look for a longer period of time. Just keep in mind that excessive retwisting might cause traction alopecia, or balding, due to the tension on your scalp.