At no time in the past or future (5)
I believe the answer is:
never
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">at no time in the past or future</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 never that I've seen before include "when pigs fly" , "Emphatic negative" , "At no time in the past or future" , "when hell freezes over?" , "Strong negative" .)