Dealing with no timestamp (Bro integration)

Yea this is just testing and they are really small (like...187k). So here's my line:

PUT /_template/bro_template
{
  "template": "bro-*",
    "mappings": {
        "bro_ts": {
          "properties": {
            "ts": {
              "type": "date",
              "format": "epoch_millis"
            }
        }
      }  
  }
}

Fingers crossed that this works!