Anastacia, that is the exact reason I learned as well. 20 mins to circulate all the blood in your body passing through your thyroid. However, like Molly said, its an interesting question as are 2 10 min pulls really the same as one 20 mins pull? The 2 differences I can see being a 30-60 second break in between changing out the oils, and of course the new oil after 10 mins vs the old.
I think I might try 2 10 mins pulls for a few days or a week to see if I can tell a difference. If anyone else wants to do the same and report back, please feel free :)