Example computing duration with aggs

script.sense

DELETE myindex
PUT myindex
POST /myindex/travel/_mapping
{
    "travel": {
        "properties": {
            "end_date": {
                "format": "dateOptionalTime",
                "type": "date"
            },
            "start_date": {
                "format": "dateOptionalTime",
                "type": "date"
            }
        }
    }
}
POST /myindex/travel/
{
    "start_date":"2013-09-11T11:50:00.000Z",
    "end_date":"2013-09-11T13:08:00.000Z"
}
GET /myindex/travel/_search?pretty
{
    "aggs": {
        "duration": {
            "histogram": {
                "interval": 1,
                "script": "(doc['end_date'].value-doc['start_date'].value)/3600"
            }
        }
    }
}