A PERIOD(TIMESTAMP(n) [WITH TIME ZONE]) value can be cast as PERIOD(DATE) using the CAST function.
Each result element is each set to the date portion of the corresponding source bound after the source bound is adjusted according to the current session time zone. The adjustment is not done for the source ending bound if that bound is the maximum value. If the adjustment for time zone changes the date, the changed value is used. If the result date portions are the same, an error is reported.