This year's CNC (http://citynaturechallenge.org/) will take place 26th to 29th April for observation recording and observation identification takes place up to 5th May. Last year observations were still accepted until the end of the id process, so long as they were observed during the observation period. I assume this is the procedure again this year.
In 2018, Hong Kong finished in 4th place for number of species observed at the cutt-off for identification, though I see now that HK ranks third after some of the identifications were fine tuned for all the participating cities..... !

The Hong Kong moth recording project (we contributed over 1,700 observations of some 380 species in CNC2018) will be taking part again, with several field sessions over the weekend of 26th-29th April. Venues are yet to be arranged, and as the weather plays an important part, the fieldwork will not take place in the event of tyhoon signals T3 or higher being in effect. Rainstorm and thunderstorm signals may also impact fieldwork.

If you are interested in attending a CNC mothing evening, please message me (@hkmoths) and I'll keep you posted.