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.
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...
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.