The longest time for Taxying - Hmm. Well one example of a bad delay between Pushback and actually getting on the Runway was at Newark, when a CRJ Pushed on Schedule and due congestion didn't make it to the runaway for take-off until an hour later, which exceeded the scheduled block time for the Flight..
That's no record - Traffic at JFK can take 3 hours taxying for departure..
as the US don't operate a a slot system. Aircraft often shut down engines to save fuel while waiting in line. Sometimes they have to return to stand to refuel!
