Date range data type showing up as unknown in Kibana

I am indexing data into ES using json

JsonObject dateRange = new JsonObject();
dateRange.addProperty("gte", startTime);
dateRange.addProperty("lte", startTime + timeTaken);

startTime and timeTaken are in epoch_millis.

Template definition for it is

"events": {
      "properties": {
        "runTimeMs" : {
          "type": "date_range",
          "format" : "epoch_millis"
        }, 

When i view the field in kibana it shows up as unknown and i am not able to filter by runTimeMs:1234. Only runTimeMs:[1 TO 3] works.

What do i need to do to make sure that runTimeMs field is of type date range and the value query works?

Date range data type is not really fully supported in Kibana, so your best choice would be to use 2 separate fields for the range and then filtering using those.