code: private String getFormattedTimestamp(int offset) {
          SimpleDateFormat df = new SimpleDateFormat(
                  "yyyy-MM-dd'T'HH:mm:ss.SSS'Z'");
          df.setTimeZone(TimeZone.getTimeZone("UTC"));
  
          if (overriddenDate != null) {
              return df.format(overriddenDate);
          } else {
              return df.format(getSignatureDate(offset));
          }
      }
docs: Formats date as ISO 8601 timestamp