Sang Hyun departing for Guam yesterday evening.
From WithSangHyun Facebook
Sang Hyun with Bae Su Bin and Ji Won
Time and dates of flight from respective airlines schedules:
If Sang Hyun had taken a direct KE flight from Seoul to Guam yesterday evening, it would have been on a 19:30 flight from Incheon, arriving in Guam around 01:00 (2nd May). If it was on a UA flight, it would have been on a 22.45 flight, arriving in Guam at 04:05 (2nd May). UA being the only airline flying from Guam to Yap Island with 2 flights per week (Tuesdays and Saturdays), it is most likely that he would be taking the 20:25 UA flight this evening and arriving at Yap Island at 22:05.
The first group had departed on Monday 27th April so probably it was to catch the Tuesday flight which coincides with the flight schedules.