http://www.umuc.edu/library/libhow/copyright.cfmIn General, What Counts as Fair Use?
Poetry
Copies of a poem of 250 words or less that exists on two pages or less or 250 words from a longer poem.

http://www.artcc.org/84032v1ACCWhitePaper.PDF
People claim, “all you have to do is change a little bit”, “a few lines here and there”, “five percent”, “ten percent”, “twenty percent”, “eight measures of music”, “250 words in a literary work”, all of these supposed guidelines are without support in the law. Ignore them, forget you ever heard them.

https://www.lib.umn.edu/pdf/CanIUseThat-Handout-03_2011.pdf
It’s also tempting to look for guidance from sources that give hard-and-fast rules: “quoting 250 words is okay”, “any video clips over 30 seconds are not fair use”. But a lot of those guidelines are too simplistic, and err on the very conservative side. To fully understand and exercise your fair use rights, you have to embrace the uncertainty with the flexibility!