GROUP 1 TO THE SEOUL SKY OBSERVATORY MUST ARRIVE BY 9:30 AM. I REALLY SUGGEST GOING EARLIER at 8:30 - no later than 9 am. Chris from The Benza/Tokyo Cowboys will be on Level ! by check-in ordering taxis. Up to 4 per taxi. Credit Card or Cash. He will have the address to give to the taxi driver. You can walk to the subway, line 8 by the Garden 5 shopping center. Leave by 8:30 if going by subway to give walk time.
Group 2 must arrive by 10:30. Leave between 9:45 and 10 if by taxi, between 9:30 and 9:45 if by subway.
Here is the link to the directions to the Lotte World Tower. DIRECTIONS