code: public DateTime minusSeconds(int seconds) {
          if (seconds == 0) {
              return this;
          }
          long instant = getChronology().seconds().subtract(getMillis(), seconds);
          return withMillis(instant);
      }
docs: Returns a copy of this datetime minus the specified number of seconds.
  <p>
  The calculation will subtract a duration equivalent to the number of
  seconds expressed in milliseconds.
  <p>
  The following three lines are identical in effect:
  <pre>
  DateTime subtracted = dt.minusSeconds(6);
  DateTime subtracted = dt.minus(Period.seconds(6));
  DateTime subtracted = dt.withFieldAdded(DurationFieldType.seconds(), -6);
  </pre>
  <p>
  This datetime instance is immutable and unaffected by this method call.
  
  @param seconds  the amount of seconds to subtract, may be negative
  @return the new datetime minus the increased seconds
  @since 1.1