Only the person testing you can tell you how long the tests they will do will take. We have no way of knowing which diagnostic tests and interview process they are going to use or how long they intend to take to administer them.
My personal diagnostic interview with the psychiatrist took 2 hours. But who knows if your will be similar or not.
It took me about three weeks to get the formal results. But yours will likely be completely different.
The only person who can answer these questions is the person who will be testing you.

Who is the "someone" who told you you will have to see a medical doctor as well? If it was random person online what the heck do they know about what your therapists etc want to do? Nothing! If it was your therapist or psychiatrist who told you you will need to see a medical professional as well then ask them who and when they want you to do that.