My sessions are for one hour, once a week. However, I occasionally find it neccesary to adjust the length and frequency of sessions to cater to the clients needs.
Regarding the length of therapy, it is completely dependant upon the complexity of the issues and the willingness of the client to engage in the therapeutic process. I have had clients who come for one session and I have clients who remain in therapy for multiple years. Ultimately, the decision is the client's.