It really depends on you and your symptoms.

I know some in the past had compression 100% of the time even with arms down.
That usually indicates a more constant compression, also mentioned was severe swelling & constant heaviness of arms.


Does PT work on overall posture?
Does PT seem to have advanced skills & knowledge of TOS?
do you have the head forward of the body and/or shoulders forward or hunched? very typical for long time desk workers.
If so, working on opening the chest and dropping the shoulders back/down might give the extra space back to a more normal.

What kind of stretches are they having you do?
Has your alignment been evaluated - perhaps by a expert chiropractor?
Especially if you have been in any accidents or sports injury with hits or falls to upper body.

Did testing/imaging show what was causing the occlusion?
Any bony anomalies?