It's easy to find: https://www.transportation.gov/airconsumer/notice-24hour-reservation https://www.transportation.gov/airconsumer/notice-24hour-res... Edit: I

It's easy to find: https://www.transportation.gov/airconsumer/notice-24hour-reservation https://www.transportation.gov/airconsumer/notice-24hour-res... Edit: I should add that I don't know if this specifically applies to Kayak, etc. I'm not sure if that's what you were specifically looking for.