Query - time4.query : {
  "dataSource": "rb_flow_f6f6bbfc-c5b7-4280-a9d4-25a222a441b5",
  "granularity": "all",
  "intervals": [
    "2016-10-25T03:00:00+02:00/2016-10-25T04:00:00+02:00"
  ],
  "filter": {
    "type": "or",
    "fields": [
      {
        "type": "selector",
        "dimension": "type",
        "value": "snmp-stats"
      },
      {
        "type": "selector",
        "dimension": "type",
        "value": "meraki"
      }
    ]
  },
  "queryType": "timeseries",
  "context": {
    "skipEmptyBuckets": "true"
  },
  "aggregations": [
    {
      "type": "longSum",
      "name": "flows",
      "fieldName": "events"
    },
    {
      "type": "filtered",
      "filter": {
        "type": "selector",
        "dimension": "type",
        "value": "meraki"
      },
      "aggregator": {
        "type": "hyperUnique",
        "name": "visitors",
        "fieldName": "clients"
      }
    }
  ],
  "postAggregations": [
    {
      "name": "visitors_float",
      "type": "javascript",
      "fieldNames": [
        "flows",
        "visitors"
      ],
      "function": "function (value, visitors) { return visitors; }"
    }
  ]
}

Result:
[
  {
    "timestamp": "2016-10-25T01:00:00.000Z",
    "result": {
      "visitors": 11259.898751496865,
      "visitors_float": "NaN",
      "flows": 25328
    }
  }
]