There are different ways to do it in java. You need a current date/time and iso format. This is one way:
You may import:
import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
and then:
Date d = new Date();
DateFormat iso = new SimpleDateFormat("yyyy-MM-dd'T'HH:mmZ");
newTestCaseResult.addProperty("Date", iso.format(d));