The quote you mentioned is the guidance given to Atos HCPs, which as I said in my previous post, we don't agree with it. You should be able to either sit or stand without alternating.
I'm afraid the law does clearly state that the activity should be carried out for 30 mins/1 hour and not hour after hour, but you would have to be able to repeat the activity in a reasonable amount of time.
Which one could argue is the same thing. It seems to me, unless there's some aspect I'm overlooking, that the context the action is performed in here is all-important and it's ignored making the question nonsensical. Could I sit/stand for any length of time in the first place? Depends. Could I repeat it in a reasonable time? Depends. What am I doing in the meantime? Is any guidance given? Am I assumed to be hung upside down by my thumbs in the interim or snug in bed asleep?