I don't know how it'll work for you. Different doctors have different ways of doing things. I'll just tell you how it was for me.
I did a full day of testing. Took about 7 hours with a lunch break. Then the lady put together all the results and gave it to the psychologist who studied the data to put together a formal diagnosis. I met up with her after a couple of weeks when she explained results, but I don't see why that couldn't have been done over the phone. She mailed me the results and that was that. You could probably get a GP to work with your ADHD meds. That's what I'll be doing.