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 1195 datapoints.)
The best day to arrive at Tokyo is Wednesday and it would be best to avoid Monday, as prices are on average 70.95% higher than on Wednesday. (Average prices, based on 1211 datapoints.)
The cheapest airline flying from Tokyo to Hong Kong is Hong Kong Express. They are 85% cheaper than Air Japan. (Average prices, based on 1211 datapoints.)
The best time to fly is at around 6. (Average prices, based on 1675 datapoints.)