Convert int to DateTime in Nest query?

I am attempting to query an ES cluster through Nest. However, I'm having an issue because my types are not matching.

This is the C# side:

As you can see CreatedTimeStamp is a DateTime.

However, this is what I receive in Postman:

Where CreatedTimeStamp is now an Int (or Long).

When I run this basic query:

var searchResponse = Event.client.Search<mdl.Event>(s => s
                    .From(0)
                    .Size(1000)
                    .Query(q => q
                        .MatchAll()));

This is causing the following error:

Elasticsearch.Net.Utf8Json.JsonParsingException : expected:'String Begin Token', actual:'1631555771000', at offset:344

Basically, how can I convert the type from ES to fit the C#?