Here are flights that Ken & Tina flight could have been on if the Pit Stop was the proper 12 hours. I'm going with a checkin time of 9:20 am on May 2nd. So they start driving to AKL at 9:20 pm on May 2nd. They reach AKL just after midnight on May 3rd. They can now take this flight sequence:
Singapore Airlines 7295 leaving AKL at 2:50 am and arriving in SIN at 8:35 am
Singapore Airlines 18 leaving SIN at 9:55 am and arriving in Seoul ICN at 5:20 pm
Asiana Airlines 737 leaving ICN at 8:00 pm and arriving in Siem Reap at 11:50 pm
or even better with this one
Singapore Airlines 7295 leaving AKL at 2:50 am and arriving in SIN at 8:35 am
Singapore Airlines 972 leaving SIN at 10:30 am and arriving in Bangkok at 11:55 am
Bangkok Airways 5915 leaving BKK at 1:10 pm and arriving Siem Reap at 2:30 pm
They would have completed the Siem Reap leg on May 3rd and be one day ahead for the outbound flights of the next leg.