Diyan is correct that we use the long date format by default but there are a couple of additional options. That element is the ScheduleViewDayHeader element. By default it contains a ScheduleDateTimePresenter where the DateTime property is bound to the element's Date property and uses the LongDate format.

1. You can retemplate that element and modify it's contents - e.g. put in a TextBlock where the Text is bound to the Date property and set the StringFormat property of the Binding to whatever format you want to use. You can use the DefaultStyles we provide as a starting point for your custom template.
2. The ScheduleDateTimePresenter and ScheduleDateRangePresenter classes use the resolved DateInfoProvider of the XamScheduleDataManager to format dates. By default the xamScheduleDataManager creates one based on the CultureInfo.CurrentCulture but you can set the DateInfoProvider property to an instance of one if you want to control what is used. Therefore you can create a class that derives from DateInfoProvider, override the FormatDate method calling the base for everything except when the DateTimeFormatType is LongDate. Note, the LongDate may be used things other than just that element and therefore this approach would affect all of those as well - e.g. the format used in the tooltip for the appointment. Then you would have to set the DateInfoProvider of the XamScheduleDataManager to an instance of your class.

Hi Urfan,

This date format is dependent on the Regional Settings of your OS since the ScheduleDateTimePresenter is using Long Date format. You can change it here: