All an IMR does is a second opinion. It will delay the process by 1-2 weeks usually. Without knowing your conditions it’s difficult to say if it would help or hurt your case. In my case it the new doctor agreed with the narsum writing doctor. My IMR thus made no difference.
Once I submitted my IMR, it only took about 2 days to get my results back from it. It did delay the process a bit but nothing substantial. Unless you have something you're concerned they may change then it probably wouldn't hurt you. They're objectively looking at the evidence that is provided to them and typically not trying to change diagnoses or anything (although they could).
