Sentence:  For example , to move ( as the score requires ) from the lowest F major register up to a barely audible N minor in four seconds , not skipping , <WSD>at</WSD> the same time , even one of the 407 fingerings , seems a feat too absurd to consider , and it is to the flautist 's credit that he remained silent throughout the passage . 
Meaning of the word marked with <WSD> tags:  at the same instant