var json = "{"timestamp":"2016-06-16T16:27:36.808Z"}";
var dict = JsonConvert.DeserializeObject<Dictionary<string, object>>(json);
Console.WriteLine(dict["timestamp"]);

16/06/2016 16:27:36

var obj = dict["timestamp"];
var timestamp = DateTime.Parse(obj.ToString());
Console.WriteLine(timestamp.ToString("yyyy/MM/dd HH:mm:ss.ffff"));

2016/06/16 16:27:36.0000

var jsonSerializerSettings = new JsonSerializerSettings { DateParseHandling = DateParseHandling.None };
var dict = JsonConvert.DeserializeObject<Dictionary<string, object>>(json, jsonSerializerSettings);
var obj = dict["timestamp"];
var timestamp = DateTime.Parse(obj.ToString());
Console.WriteLine(timestamp.ToString("yyyy/MM/dd HH:mm:ss.ffff"));

2016/06/16 17:27:36.8080

var json = "{"timestamp":"2016-06-16T16:27:36.808Z"}";
var dict = JsonConvert.DeserializeObject<Dictionary<string, object>>(json);
Console.WriteLine(((DateTime)dict["timestamp"]).ToString("O"));