Depends on the kind of case. If you need to get on medication on priority, then my first task will be to help you get to the doctor, and as such, significant progress can be made in the first session itself.
I suggest you stay open to investing in 1-3 sessions the first time you contact me. At the end of the first session, I will share my sense of how long we may need to work together. We can decide on bi-weekly, weekly or fortnightly sessions, depending on your emotional and financial situation, as well as your inclination.
You should see significant progress by the 3rd session, and should be feeling that therapy is now optional or good-to-have rather than needed by the 10th-12th session.