To my knowledge I know of no Army Regulation that covers this requirement. This is usually a local policy. For example each installation or post usually has a list of standards that are in addition to Army regulations and policies. I have attached an example of one from Fort Hood for you review.
Please look at page 15-16 as I believe it contains information pertaining to your situation. Here is an extract:
The following rules apply in most situation you are likely to face
(1) Unit Headquarters, Orderly rooms, Supply rooms, dayrooms, squad rooms. The first person to see an officer who is higher rank than the officer present in the in room should call “ATTENTION”. The senior Soldier present in the area should then report to the visiting officer. In smaller rooms, containing one or two enlisted Soldiers, the Soldier(s) should rise and sand at the position of attention when an officer enters the room.
