Korean securities firms plan to offer nearly 24-hour U.S. stock trading services starting December 6, enabled by combining Nasdaq's expanded 23-hour trading session with an additional hour provided by alternative trading system Blue Ocean. According to financial industry sources, South Korean brokerages and the Korea Securities Depository (KSD) are making preparations for the launch, with the KSD set to step up monitoring and ensure smooth settlement through its custodian bank, Citibank.