Incorrect, only if one do it more than 24 hours, you don't need same fare class being available to do confirmed, as there is NO WAY anything lower than H being available 24 hours prior to departure on any flights any airlines.

Not apply to OP, as there is only one ORD-HKG per day, nothing else to standby

Incorrect again, when one do OLCI 24 hours prior to the flight, usually on united.com under your schedule flight, it would have a button that said "other flight options", if you click on it, it would have other options for confirmed flights being available earlier or later than your original flight, sometimes even have flights the night before. You can choose which flights has the best seat avaialble to decide which one you can to confirmed on, if you don't like the option, then you can just cancel the option.