How many letters does the top answer for “a small amount or duration” have?

The most common answer is little (6 letters).

Crossword clue: a small amount or duration

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

little 6 letters wn-def

limited or below average in number or quantity or magnitude or extent

a small amount of residue 50% similar → dreg

a small and inadequate amount 50% similar → scarceness, scarcity

a small worthless amount 50% similar → diddley, diddly, diddlysquat

contemptibly small in amount 50% similar → measly, miserable, paltry