[cperciva]

In the latter case, the delay window is up to 4 hours, which seems unlikely barring some natural catastrophe

It's unlikely that one flight will be over 4 hours late; but the delay time which matters is based on when you reach your final destination. For example, a few years back I was flying LHR-YUL-YVR; the flight from London to Montreal was only 1.5 hour delayed, but that was enough that I missed the last flight of the day from Montreal to Vancouver, and qualified for compensation based on my arrival in Vancouver being 10 hours late.

[lutorm]

Indeed. We flew from Stockholm to Hawaii and the SAS flight was late out of Stockholm, which cascaded to us being a full 24h late (same flight next day) to our destination in Hawaii. We got reimbursed without a problem and since we were traveling with an infant it was actually kind of nice to get a free full nights sleep in a hotel near LAX...