Currently, when parsing a VTIMEZONE's RRULE component in ICalTimeZones, RecurrenceRule::timesInInterval() returns no values. This is due to KDateTime::isValid() wrongly returning invalid for an instance which is specified in ClockTime, if the date/time is invalid in LocalTime. This in turn is due to QDateTime being set to Qt::LocalTime, and unlike in Qt4, QDateTime in Qt5 uses the local time zone to validate the date/time. For ClockTime, there is no associated time zone, so it should ignore the local time zone when validating.
In this particular case, the time being validated is the time in the previous daylight saving or standard time at which the transition to the next daylight saving/standard time takes place. For a transition to daylight saving, this is by definition invalid in the local time zone, and in any case it could be for any time zone (not the local one).