How many letters does the top answer for “the property of not existing for indefinitely long durations” have?

The most common answer is impermanence (12 letters).

Crossword clue: the property of not existing for indefinitely long durations

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

impermanence 12 letters wn-def

the property of not existing for indefinitely long durations

impermanency 12 letters wn-def

the property of not existing for indefinitely long durations