Can derivative warrants or CBBCs be traded during closing auction session?

No, both derivative warrants and CBBCs are not eligible for trading in closing auction session and their market closing time is 4:00 p.m.

However, some underlying securities are eligible for trading in closing auction session and the closing level of the relevant index will be ascertained after 4:10 p.m. (or 12:10 p.m. in the case of half day trading) (“eligible underlying asset”). As a result, the market closing time for a derivative warrant or CBBC and its underlying asset can be different. In this case, the price or level of eligible underlying assets may move in closing auction session while investors cannot buy or sell related derivative warrants or CBBCs. Moreover, the CBBC can be knocked out and mandatory call event will occur if the closing price or level of the eligible underlying asset hits the call price or level at the end of the closing auction session.

You may read further "I hold a bull CBBC linked to an HSI constituent stock. The CBBC was still trading until close of the market at 4:00 p.m. I noted that the CBBC was knocked out subsequently at around 4:10 p.m. How could the CBBC be knocked out after market close at 4:00 p.m.?" .