Field value not updating when posting data via JSON
You should be adding your date in the value property and not including a time.

"field_date_of_cage_card_creation": {
    "und": [
        {
            "value":"17 Dec 2018",
            // or maybe
            "value":"2018-12-17",
            "timezone": "Asia/Kolkata",
            "timezone_db": "Asia/Kolkata",
            "date_type": "datetime"
        }
    ]
},