zero hour
noun [ U ] uk/ˈzɪə.rəʊ ˌaʊər/ us/ˈzɪr.oʊ ˌaʊr/
行动开始时间；（尤指军事行动的）发动时刻
the time at which something, especially some type of military activity, is planned to begin
Indian English（印度议会的）自由问答时间
in the Indian parliament, the time during which members of parliament can ask questions without arranging to ask them first