Very brief moment (5,6)
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">very brief moment</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for split second that I've seen before include "Twinkling of an eye" , "Very little time" , "Very brief moment of time" , "An extremely short time" , "Instant" .)