"dark thirty" meaning in English

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "dark thirty (uncountable)",
      "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": "Times of day",
          "orig": "en:Times of day",
          "parents": [
            "Periodic occurrences",
            "Timekeeping",
            "Time",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "Synonym of oh dark thirty"
      ],
      "id": "en-dark_thirty-en-noun-5yfqawvj",
      "links": [
        [
          "oh dark thirty",
          "oh dark thirty#English"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "oh dark thirty"
        }
      ],
      "tags": [
        "uncountable"
      ]
    }
  ],
  "word": "dark thirty"
}

{
  "head_templates": [
    {
      "args": {
        "1": "-"
      },
      "expansion": "dark thirty (uncountable)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "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 uncountable nouns",
        "en:Times of day"
      ],
      "glosses": [
        "Synonym of oh dark thirty"
      ],
      "links": [
        [
          "oh dark thirty",
          "oh dark thirty#English"
        ]
      ],
      "synonyms": [
        {
          "tags": [
            "synonym",
            "synonym-of"
          ],
          "word": "oh dark thirty"
        }
      ],
      "tags": [
        "uncountable"
      ]
    }
  ],
  "word": "dark thirty"
}