How many letters does the top answer for “the quality of being constantly diligent and attentive” have?

The most common answer is sedulity (8 letters).

Crossword clue: the quality of being constantly diligent and attentive

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

sedulity 8 letters wn-def

the quality of being constantly diligent and attentive

sedulousness 12 letters wn-def

the quality of being constantly diligent and attentive