Your format doesn't conform with Built-in formats of Elastic Search 2.3! Please refer 'Built In Formats' under https://www.elastic.co/guide/en/elasticsearch/reference/current/mapping-date-format.html
I did face exactly the same issue! But I tweaked my PHP time object's format to be in accordance with Elastic Search Mapping!
Curl command to create mapping for the the field 'ClickTime' in a standard format :
curl -XPUT localhost:9200/telemetry/_mapping/DashBoardVisits?
pretty -d "{"properties" : {"ClickTime" : {"type" :"date" , "format" :
"yyyy-MM-dd HH:mm:ss" }}}"
PHP code to create a time object matching the type and format of 'ClickTime' in Elastic Search :
$curtime = date_create();
$kibanadate = date_format($curtime,"Y-m-d H:i:s");