Axis.MinorUnitScale (PowerPoint)
Returns or sets the minor unit scale value for the category axis when the CategoryType property is set to xlTimeScale. Possible return values are xlDays - Days, xlMonths - Months, xlYears - Years.
MinorUnitScale can be one of the following xlTimeUnit constants:
ActivePresentation.Slides(1).Shapes(1).Chart.Axes(1).MinorUnitScale = xlDays