Major depressive disorder is said to occur when signs of depression last at least

Two Weeks

Explanation:

Major Depressive Disorder or simply Depression is a serious mental disorder characterised by periods of low, sunken moods, withdrawal and lack of interest in everyday activities like talking, eating, socializing.

The will to stay alive begins to gradually ebb as the victim is no longer interested in life and begins to withdraw from people.

The victim may also start hallucinating by seeing or hearing things that do not exist.

However for a person to be confirmed as depressed, the symptoms must have lasted for a minimum period of two weeks