Trip length is not pass length
A five-night Seoul stay does not automatically justify 120 hours. The pass clock begins with the first free-attraction use and runs continuously, so arrival, departure and rest time can sit outside the useful block. Build the sightseeing block first, then choose the smallest pass that contains it.
The upgrade must buy real value
The current official prices put a ₩40,000≈£21.1 difference between the 72-hour and 120-hour products. The longer product earns that difference only when the extra days add more than ₩40,000≈£21.1 of eligible benefits you would otherwise purchase—or create enough practical flexibility to justify a non-financial premium.
Opening days can break a theoretical win
A spreadsheet can place every attraction inside 72 hours while the real week cannot. Confirm live attraction participation, opening days, reservation requirements and travel time. If moving one closed attraction destroys the saving, the result is fragile and individual tickets or Pick 3 may be safer.