Generally people start to feel better in about 4-6 weeks time. Sometimes it may take up to 6 Months to see full improvement. One must bear in mind that medication is just one aspect of the treatment. Hence it is important to  a ensure that the individual has stable and supportive environment without additional stress/anxiety apart from wish to overcome depression. Alcohol/drugs in the picture may delay recovery as medications may not work with alcohol/drugs. Best wishes.