generally safe until midnight the next day. In my prior experience, you can sometimes get an agent to give you the price even if the online price it quotes changes on a held reservation (then you will have to pay the agent ticketing fee).


also the 11:59pm is usually based on the time zone of departure. So a ticket departing from Japan would be 11:59 JST, Dallas 11:59 CST, NY 11:59 EST.