Hey NF,
I wish you much luck in applying for SSDI. You will probably get all kinds of responses as to how much time it takes to receive SSDI. There are a lot of variables with each individual.
I can tell you that it only took 5 months and I did not need an atty. I filed all the paperwork myself. It's extremely important to fill out your paperwork completely and fully explain what you jobs have entailed physically/mentally and why you cannot do them anymore. The more info, the better!
Here are some links to our sister site, NeuroTalk that I found to be totally helpful:
http://neurotalk.psychcentral.com/thread148967.html
http://neurotalk.psychcentral.com/thread120255.html
http://neurotalk.psychcentral.com/thread367.html
It's also a good idea to stay on top of your doctor's offices to make sure they file the paperwork in a timely manner to SSDI. I know that's one issue that can stall their decision if it's not received quick enough.
I consider myself to be one of the real lucky ones to not have to wait more than the 5 month period. SSDI says it normally takes 3 to 5 months for a decision. Unfortunately, there are so many who wait much longer than that for a decision and have to jump through hoop after hoop during that time.
I think what was key for me to get a quick decision was my age. I'm 56 and anyone 56 and older seems to have an easier time because they feel that age plays a big role in their decisions as well.
I wish you much luck in your application process and determination. It's stressful to say the least, but hang in there....