J.S.
You should get results the first day but understand adderall is known for causing anger in some. My kids took it just fine but I have heard others have had issues.
I like myself just fine sounds like an odd thing for a seven year old to say, even one without ADHD. You may want to make sure someone in his life, you, dad, grandparents, aren't against the meds. That is about the only way I see those words coming out of your son's mouth, someone planting them.
You also need him to learn to take pills. I would have lost my mind if my kids hadn't mastered that by kindergarten. Too hard to keep finding stuff to hide it in, every freaking day. The beauty of pills, they taste like whatever you are taking them with. By the way my kids learned that by three so he is not too young to master pill taking.
Good like and monitor the anger. If it is constant he may need to try a different stimulant.