Also with the upper body the time away from actively mobilising it is crucial.
I used to:
- sleep on my side, half twisted.
- sit over my meals
- jump on the train, lean on the wall, head angled down, reading or looking at my phone
- get to work, almost lay in my seat rather than sit in it
- get home and slouch into the couch
- never holding my shoulders back.
Then wonder why 10 minutes upper body stretches per day wasn't sorting me out?
Also, one exercise I really like is standing up, bend at the elbow, hand behind your back so your Palm is facing away from your lower back and your upper arm is along side you.
Bring the elbow in line with your wrist (you can use a wall to get a stretch), make sure your shoulder does track forward and your posture is good.