Sometimes a problem needs only a few sessions before things start to feel much more positive. There are times when problems need a bit longer. I have worked with people therapeutically in time frames from anywhere between two- three weeks and a year. I think it is something that needs to be decided between the therapist and the individual within the first two sessions. This can then be reviewed regularly. I prefer to be honest about what I think people need.  I would also much rather be told if a person has a specific time frame in mind.