How many letters does the top answer for “the property of lasting for a very short time” have?

The most common answer is ephemerality (12 letters).

Crossword clue: the property of lasting for a very short time

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

ephemerality 12 letters wn-def

the property of lasting for a very short time

fleetingness 12 letters wn-def

the property of lasting for a very short time

lasting a very short time 80% similar → ephemeral, fugacious, passing

the property of lasting only a short time 67% similar → temporariness

for a very short time 60% similar → transiently