In my State of Tennessee the average is right at 3 years if you have to take it all the way to a hearing. Many people win on there first completion of paperwork. Depends on your diagnosis.
As Cavaliers stated... You do have to be very mindful of how you answer any questions on paperwork as they are designed to trip a person up.. The basic same question can be asked many different ways , but the answers must all add up or it can be a quick denial.
Good luck