I don't know very many people on SSID, but the two people that I do know, their processes were completely opposite.
One took several years and several appeals, she had a disease that is not very well known, so its not listed in the list of diseases that qualify under the disability protocol. When she finally had a hearing during her second appeal, and went before judge, she had one of her episodes (called a neuro storm) during her hearing and the judge was frightened and finally approved her benefits.
The other one took a few months. The application was filed in June and approved in August. The case manager said that is about the fastest case that she had ever seen. The person technically could have filed for disability years prior but had been working anyway, between long absences on short term disability. His disease is somewhat common, listed as qualifying for disability, and he had years of records, thousands of pages of documents on the treatment and amount of time he had missed work over the years because of his illness.