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.
I my case I recieved the max compensation because i got delayed a bit over an hour on the first leg of the flight due to problems in loading luggage, which made me miss the connecting flight overseas. Total delay was 10hours. Took them almost a year to pay me back (Lufthansa)
I might not have bothered, except they had us waiting for almost 12 hours in the airport, then another 12 hours the next day.