I have internally rotated humeri.
I believe that when a muscle is stretched it is weak and inactive. Like the glutes and hamstrings in a bad case of anterior pelvic tilt. Am I correct?
I assume because I have internally rotated humeri I have hyperactive pectorals. Am I correct?
The fact that I have hyperactive pecs leads me to believe that my rear delts are in a stretched state and mostly inactive during horizontal pulling movements.
I feel that if I stretch the pectorals for 2 minutes a side and then do bat wings right after that I will see noticeable change in my rear delts and possibly my posture.
you are pretty much correct. However, it’s more likely that your external rotators and upward rotators are weak. While your rear delts do fall into those categories, they are only a small part of the puzzle, and not IMO the most important.
Strengthen your upper back. Lots of external rotation and upward rotation, and I do mean LOTS of upward and external rotation. Do it every day and as part of your warm up in the gym.
I don’t put a lot of stock in stretches to be honest, but you could try stretching your pec minor. It certainly won’t do any harm. 2 minutes in one go is probably overkill.
I agree with rds63799’s advice.