Add date to each new created entry in Elasticsearch

I read this post, but the timestamp is depreciated. And I am still not fully up to speed on what to do.

I have Logstash passing logs to ES with ES's Dynamic Field Mapping (I believe this is the correct terminology). But I still don't know how to add the date index on creation, even after considerable reading. I have tried to ask in irc, but get a comment here and a comment there and for someone that is new to this topic, there is little help to be found, so I am trying here.

My unsuccessful final attempt was:

curl -XPUT localhost:9200/_template/my_template -d '
    "template" : "log*",
		"mappings": {
		    "type1": {
		      "properties": {
		        "created_at": {
		          "type": "date",
		          "format": "yyyyMMdd'T'HHmmss.SSSZ"

I deleted the logstash dynamic template, so it would start again, but nothing has changed!

Can some please assist, so I can make some ground? Thanks in advance.