You can compare UNTIL_CHANGED only to the ending bound of a Period value with an element type of DATE or TIMESTAMP WITH TIME ZONE. Therefore, the result type of the END function must be DATE or TIMESTAMP WITH TIME ZONE. See END.
In comparisons, the precision of the UNTIL_CHANGED value is truncated to the precision of the ending bound value being compared. That is, the number of digits after the decimal point for UNTIL_CHANGED depends on the precision of the ending bound value. The time zone is omitted if the ending bound value has no time zone.
If the ending bound value is NULL, IS [NOT] UNTIL_CHANGED returns UNKNOWN.
You cannot use IS [NOT] UNTIL_CHANGED on the ending bound of a system-time or temporal table columns.