code: public static Seconds secondsBetween(ReadablePartial start, ReadablePartial end) {
          if (start instanceof LocalTime && end instanceof LocalTime)   {
              Chronology chrono = DateTimeUtils.getChronology(start.getChronology());
              int seconds = chrono.seconds().getDifference(
                      ((LocalTime) end).getLocalMillis(), ((LocalTime) start).getLocalMillis());
              return Seconds.seconds(seconds);
          }
          int amount = BaseSingleFieldPeriod.between(start, end, ZERO);
          return Seconds.seconds(amount);
      }
docs: Creates a <code>Seconds</code> representing the number of whole seconds
  between the two specified partial datetimes.
  <p>
  The two partials must contain the same fields, for example you can specify
  two <code>LocalTime</code> objects.
  
  @param start  the start partial date, must not be null
  @param end  the end partial date, must not be null
  @return the period in seconds
  @throws IllegalArgumentException if the partials are null or invalid