        1. Let _timeZone_ be ? ToTemporalTimeZoneIdentifier(_item_).
          1. Let _temporalTime_ be *undefined*.
        1. If _temporalTime_ is *undefined*, then
          1. Let _epochNs_ be ? GetStartOfDay(_timeZone_, _plainDate_.[[ISODate]]).
        1. Else,
          1. Set _temporalTime_ to ? ToTemporalTime(_temporalTime_).
          1. Let _isoDateTime_ be CombineISODateAndTimeRecord(_plainDate_.[[ISODate]], _temporalTime_.[[Time]]).
          1. If ISODateTimeWithinLimits(_isoDateTime_) is *fal