I've got the latest version of Postman for Windows (6.3.0 at the moment).
Somehow it now returns timestamps as a number of Unix seconds (like this 1852502400.000) instead of DateTime in format YYYY-MM-DDThh:mm:ss[.sss]Z.
Server-side is microservice written in Java, type of the field is java.time.OffsetDateTime.
Is there something in Postman I should configure, or is it depends from server implementation?
You can always use javascript to help you with this.
Make use of the environment variable and add the variable in place of the {{$timestamp}} in your request.
In your pre-request script do this:
let timestamp = new Date().toJSON();
pm.environment.set('timestamp', timestamp);
Now, wherever in your request that you were using {{$timestamp}} replace it with {{timestamp}}.
Just run the request and you'll get the date in this format: "2018-09-13T18:41:02.363Z"
Additonal information: Postman also has MomentJS builtin. So you can make use of that too.
Danny Dainton has written a great blog on how to use momentjs inside postman: https://dannydainton.com/2018/05/21/hold-on-wait-a-moment/ !
Postman sandbox API reference: https://www.getpostman.com/docs/v6/postman/scripts/postman_sandbox_api_reference