for the long haul vs how long

for the long haul

adv

  • For a long time; for an extended period or duration; all the way 

how long

adv

  • Used literally: for what duration. 

adj

  • Used literally: what duration. 

  • Used literally: what length. 

How often have the words for the long haul and how long occurred in a corpus of books? (source: Google Ngram Viewer )