Looks like the final rule starts on pg. 246 of the pdf.

Interesting that the definition of "significant change" references scheduled delays, but not actual delays (unless I'm missing something?). I wonder if airlines can get around the whole rule just by leaving the schedule as is and letting the flight run hours late? Reading the comments and responses to the proposed rule, it's clear that's not the intent, but I'm surprised the DOT didn't throw something in there about the time that the flight actually departs or arrives.