"zero hour" meaning in English

{
  "forms": [
    {
      "form": "zero hours",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "zero hour (plural zero hours)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English entries with topic categories using raw markup",
          "parents": [
            "Entries with topic categories using raw markup",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "English terms with non-redundant non-automated sortkeys",
          "parents": [
            "Terms with non-redundant non-automated sortkeys",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Zero",
          "orig": "en:Zero",
          "parents": [
            "Numbers",
            "All topics",
            "Terms by semantic function",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "examples": [
        {
          "ref": "1929, Sir Arthur Conan Doyle, When the World Screamed",
          "text": "I waited with occasional glances at my watch until the zero hour should arrive.",
          "type": "quotation"
        },
        {
          "ref": "1937, Siegfried Sassoon, The Complete Memoirs of George Sherston, London: Faber, page 339 (1972 paperback edition)",
          "text": "Zero hour was forty-five minutes after midnight. Two companies were to attack on a 600-yard front …",
          "type": "quotation"
        },
        {
          "ref": "1972 April 17, Elton John, Bernie Taupin, “Rocket Man”, in Honky Château, performed by Elton John",
          "text": "She packed my bags last night, pre-flight / Zero hour 9 a.m. / And I'm gonna be high / As a kite by then",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Synonym of H-hour."
      ],
      "id": "en-zero_hour-en-noun-SPT~Kb1n",
      "links": [
        [
          "H-hour",
          "H-hour#English"
        ]
      ],
      "related": [
        {
          "word": "D-Day"
        },
        {
          "word": "X-Day"
        },
        {
          "word": "zero-hour contract"
        }
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "H-hour"
        }
      ],
      "translations": [
        {
          "code": "nb",
          "lang": "Norwegian Bokmål",
          "sense": "Translations",
          "word": "klokken H"
        },
        {
          "code": "pl",
          "lang": "Polish",
          "sense": "Translations",
          "tags": [
            "feminine"
          ],
          "word": "godzina zero"
        }
      ]
    }
  ],
  "word": "zero hour"
}

{
  "forms": [
    {
      "form": "zero hours",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "zero hour (plural zero hours)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "related": [
    {
      "word": "D-Day"
    },
    {
      "word": "X-Day"
    },
    {
      "word": "zero-hour contract"
    }
  ],
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English entries with topic categories using raw markup",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "English terms with non-redundant non-automated sortkeys",
        "English terms with quotations",
        "Translation table header lacks gloss",
        "en:Zero"
      ],
      "examples": [
        {
          "ref": "1929, Sir Arthur Conan Doyle, When the World Screamed",
          "text": "I waited with occasional glances at my watch until the zero hour should arrive.",
          "type": "quotation"
        },
        {
          "ref": "1937, Siegfried Sassoon, The Complete Memoirs of George Sherston, London: Faber, page 339 (1972 paperback edition)",
          "text": "Zero hour was forty-five minutes after midnight. Two companies were to attack on a 600-yard front …",
          "type": "quotation"
        },
        {
          "ref": "1972 April 17, Elton John, Bernie Taupin, “Rocket Man”, in Honky Château, performed by Elton John",
          "text": "She packed my bags last night, pre-flight / Zero hour 9 a.m. / And I'm gonna be high / As a kite by then",
          "type": "quotation"
        }
      ],
      "glosses": [
        "Synonym of H-hour."
      ],
      "links": [
        [
          "H-hour",
          "H-hour#English"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "H-hour"
        }
      ]
    }
  ],
  "translations": [
    {
      "code": "nb",
      "lang": "Norwegian Bokmål",
      "sense": "Translations",
      "word": "klokken H"
    },
    {
      "code": "pl",
      "lang": "Polish",
      "sense": "Translations",
      "tags": [
        "feminine"
      ],
      "word": "godzina zero"
    }
  ],
  "word": "zero hour"
}