Portion of time (6)
I believe the answer is:
period
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">portion of time</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for period that I've seen before include "Stretch of time" , "Length of time, or a full stop" , "Stop in America" , "Span of time" , "term" .)