How many letters does the top answer for “a musical note having the time value of a sixty-fourth of a whole note” have?

The most common answer is hemidemisemiquaver (18 letters).

Crossword clue: a musical note having the time value of a sixty-fourth of a whole note

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

hemidemisemiquaver 18 letters wn-def

a musical note having the time value of a sixty-fourth of a whole note