I applied for SSI in January 2006, was denied two times and appealed both times. I finally was approved in April 2009 after I went before a judge for the hearing. The hearing took about 10 minutes and I was approved. My attorney told me that it was the one of the quickest decision that he had been involved which basically means that I should have been approved the first time I filed. It also depends on the state you are in because in Ohio it takes at least 2 years to get a hearing with a judge. So most of my time was spent on waiting for the hearing. As I said before, I really should have been approved the first time I applied because my condition and treatment plan remained the same from the day I applied until the day of my hearing.
If you do apply and are denied, don't give up. Keep appealing. You may even get approved the first time as some people I have spoken with that have MG were approved when they first applied.
I was blessed in the fact that I had continued a disability insurance policy from a previous employer and they approved my disability when I filed with them so I was receiving monthly payments from them while I waited for my SSI to be approved. I kept thinking to myself if the company that held my private disability policy approved me right away then why in the world didn't Social Security???
Different guidlines I guess and also it is different when you are dealing with the Government.
Good luck in whatever you decide to do.