code: private long readTimeStamp(byte[] buffer, int offset) {
          long seconds = read32(buffer, offset);
          long fraction = read32(buffer, offset + 4);
          return ((seconds - OFFSET_1900_TO_1970) * 1000) + ((fraction * 1000L) / 0x100000000L);
      }
docs: Reads the NTP time stamp at the given offset in the buffer and returns
  it as a system time (milliseconds since January 1, 1970).