How many letters does the top answer for “check a second time” have?

The most common answer is countercheck (12 letters).

Crossword clue: check a second time

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

countercheck 12 letters wn-def

something that checks the correctness of a previous check

to cross a second time. 50% similar → recross

to issue a second time. 50% similar → reissue

to order a second time. 50% similar → reorder