BTW one solution if you want to ensure UTC DateTime’s are serialized in a ISO 8601 format is to take over serialization of DateTime with:
JsConfig<DateTime>.SerializeFn = date =>
date.ToUniversalTime().ToString("o", CultureInfo.InvariantCulture);
JsConfig<DateTime?>.SerializeFn = date =>
date.Value.ToUniversalTime().ToString("o", CultureInfo.InvariantCulture);