Hello, number of days can't be determined in case of any therapeutic modality. However it is advisable to seek proper professional help when it comes to mental health issues such as depression. There are several people who claim to be hypnotherapist through some certification however lack proper knowledge of clinical psychology. So chose your therapist wisely by making sure the person holds a degree in clinical psychology apart from being trained in hypnotherapy.
While hypnotherapy can help in overcoming emotional issues, one first needs to determine the severity of depression, based on which sometimes medication may also be required for which you need to see a psychiatrist as well.
Next Steps
consult a clinical psychologist trained in hypnotherapy.