Fantastic couple of hours!
Very well organised, very enjoyable and lots of space, didn't feel crowded. Two decks, 350m 450m, drinks and facilities on all decks. Good value gift shoppe! Allow maybe 2 hours? Lots of coffee shops in the adjacent shopping complex. Go at around an hour before sunset to get the obvious benefits and contrast. Highly recommended.
Go in the evening!
The view was astonishing! Got to see the sunset and the night lights of Tokyo gradually lighting up. It felt like a dream to me. Unfortunately, we did not get to see Mt. Fuji because of the humidity but we did not mind at all. What we saw was already stunning and I couldn't ask for more. (A kind man said to us that they rarely see the mountain during the summer.)
Definitely a must visit! Ideally during the evening!