The date the judge set as the onset of disability for me was the date I wrote down, and that was the next day after I was let go from the casino. This was a full 2 years before I even applied, and this allowed me to have SSDI instead of SSI, which I am very grateful for. I believe the judge believed me that I couldnt work anymore, because I did not work another day after that date.
It is a good idea to have someone help you with this, I believe how you fill out the application carries alot of weight in whether you will be approved right away or not. I wish I would have known this when I applied