ES-dateformat.json

DELETE my_index
PUT my_index
{
  "mappings": {
    "my_type": {
      "properties": {
        "last_viewed": {
          "type": "date",
          "format": "dd/MM/YYYY||YYYY/MM/dd"
        }
      }
    }
  }
}

POST my_index/my_type
{
  "last_viewed": "20/10/2017"
}
POST my_index/my_type
{
  "last_viewed": "25/10/2017"
}

GET /my_index/_search
{
  "query": {
    "range": {
      "last_viewed": {
        "gte": "2017/10/15",
        "lte": "2017/10/21"
      }
    }
  }
}