So short listening of specific passages is preferable to long term listening due to adaptation to the sound.
(I also think that such adaptation is mistaken for burn in, where people advise listening to something to get used to it and so often it results in an 'improved sound'.)
Past few posts everyone is talking about something different. So everyone is right, just not right in saying the other person is wrong.
The longer you listen to a headphone though the better you should become accustomed to its sound. Which is why break in is psychoacoustic. If you look at graphs of brand new headphones, and then ones that have been used for hundreds of hours, they don't change at all. Or if there is a change, it is so small it could be due to the placement of headphone. (like .1 of a decibel)
To be able to compare two headphones on a purely sensory basis (with as little audiophile banter as possible) it would have to be quick, exactly, so you do not adapt, and are not working with anything other than sensory memory.
The comparison of sensory memory would actually put cable believers at a great advantage biologically, to detect changes if they were actually there. But, most cable believers say such tests are riduculous.