A week or less. Nightmares and vivid dreams can start in the first 1-2 days of withdrawal, generally are improved at 3-5 days and should be gone in a week. Appropriate medication, usually benzodiazepines, can reduce the complications of withdrawal. If this is you we are talking about, the major concern should be how not to drink any more. A counselor or your doctor can help. Very few people succeed on their own.