When Homeland Security reviews a Waiver application, they are looking at your criminal record. That date shows the date you were convicted. Obviously you were charged well before that date.
If I were writing a person letter for a client who was 30 months since the conviction, I would emphasize that "i had realized when arrested that I had to change my life" and then go on to make sure I emphasized the date of arrest in my personal letter, even mentioning I was arrested 3 and a half years ago, and that when I fully realized I had to make a change.
It sounds counter intuitive, but drugs or alcohol help. When you are addicted or abusing a substance, you can at least point to stopping those substances to helping you change as a person. When you are sober, then exactly WHAT did you change from the point that you were arrested that convinces anyone you are a "different person"?
Remember, thats why the Waiver is being granted. Because your offences no longer reflect you.
And for a 50/50 application like yours (your chances are 50/50 at best) every other document and information and forms should be PERFECT. Letters of reference should be BETTER than normal.
If you are not the type to have a great attention to detail, hire someone who is. At least for the first application.