Grafana not picking timestamp field while setting up data source

When I am trying to configure data source (Elasticsearch version-5.4), timestamp field is not getting resolved.
I have two timestamp field in my index :
1. “_updated_at”: "2020-10-07T16:04:22.39666202Z"
2. “start_date”: "2020-07-26"

I can create data source using “start_date” field but unable to do so using “_updated_at” field. I want to use “_updated_at” field only for date histogram purpose. Is there any limitation of Grafana in identifying zonedTimeDate having milliseconds upto 8 digits ??

you have to use the same time base

Thank you @melrose for your response. I have found the reason why “_updated_at” field wasn’t treated as timestamp one. The solution is : The field name should be as per naming convention (probably like in Java). I have changed field name to “updated_at” and it worked!