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 November and the most expensive month to fly is May. (Average prices, based on 926 datapoints.)
The best day to arrive at Tokyo is Wednesday and it would be best to avoid Friday, as prices are on average 119.6% higher than on Wednesday. (Average prices, based on 296 datapoints.)
The cheapest airline flying from Tokyo to Hong Kong is Hong Kong Express. They are 87% cheaper than Japan Airlines. (Average prices, based on 945 datapoints.)
The best time to fly is at around 2. (Average prices, based on 1244 datapoints.)