The timePeriod attribute on the DayPropertyType has a data type of TimePropertyType. The following attributes describe how this data type is constructed.
TimePropertyType attributes
Constraints:
A TimePropertyType shall have at least one of timeRange, or namedTime.
When namedTime = All Day, no other values for namedTime or timeRange shall be populated.
namedTime
These are named time periods that do not relate to the same time each day.