property Schedule.AllowUpdateAllDayFlag as Boolean
Indicates if the All-Day flag for the events being moved using drop and drop are updated once the user drops the selection.

Boolean A Boolean expression that specifies whether the AllDayEvent property is changed when the user drags and drops an event from All-Day header to Time-Scale section of the schedule view, and reverse.
By default, the AllowUpdateAllDayFlag property is True, which means that the AllDayEvent property of the event being dragged is updated once the user drops the event to All-Day header or Time-Scale part of the schedule view. The AllowUpdateAllDayFlag property has effect only if the ShowAllDayHeader property is True. The AllowAllDayEventScroll property gets or sets a value that specifies whether the all-day event header supports scrolling.

The following screen shot shows the All-Day events on the All-Day header ( ShowAllDayHeader property is True ):