@marlow7 The best place to get in stretching/mobility at work is in a
handicap bathroom stall. Those vertical bars are absolutely amazing for stretching out your shoulders. Grab it with one arm and just work out all the tight areas. Rotate your hips, kneel, turn away...do whatever it takes to open up those shoulders. Reverse your grip and do it again.
Of course, there is also room to do other things like holding a squat or Russian baby makers.
Obviously, don't be a jerk and take up the stall if someone clearly needs to use it. Keep an ear out. But in my experience, a 5-minute block of time is perfectly acceptable.