We pick the 20:00-22:00 timeslot, arrived around 20.30. It was wed night, but we still have around 15 min queuing for the tower lift. The bubble tram is quite a unique experience, it has around 45 min queue. The tram goes one round about 20 min, for 6 persons per carriage. So we spent most of the time queuing and it's already 10 pm when we finished the tram ride and directly go back to hotel. We didn't have enough time for the observation deck at all. Perhaps it's better to choose earlier time