Please be aware that Tokyo has multiple airports and that these results are for all airports serving the city.
The best month to fly between Tokyo and Hong Kong is September and the most expensive month to fly is February. (Average prices, based on 1301 datapoints.)
The best day to arrive at Tokyo is Wednesday and it would be best to avoid Monday, as prices are on average 52.4% higher than on Wednesday. (Average prices, based on 615 datapoints.)
The cheapest airline flying from Tokyo to Hong Kong is Hong Kong Express. They are 78% cheaper than Japan Airlines. (Average prices, based on 1320 datapoints.)
The best time to fly is at around 21. (Average prices, based on 1690 datapoints.)