Option to assign the timestamp automatically when post data without timestamp

Elastic Stack Elasticsearch
1

I'm trying to create index/type pattern in Elasticsearch to timestamp get automatically updated/appended/assign when I post the data without timestamp.

Means, it will automatically append the timestamp with each record based on ELS timezone. Is there any option available ?.

2

Here, Updating my config,

Problem, here is when I go Kibana4 and trying to create a "Configure an index pattern" there is no at "Time-field name". So I'm unable to move further on this. Please someone help me on this.

{
"mappings": {
"default": {
"_timestamp": {
"enabled": true,
"store": true
}
},
"myindex": {
"properties": {
"testtype": {
"properties": {
"data1": {
"properties": {
"data_value": {
"type": "string"
},
"client_ip": {
"type": "ip"
}
}
}
}
}
}
}
}
}