Axis.MajorUnitScale (PowerPoint)
Returns or sets the major 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.
MajorUnitScale can be one of the following xlTimeUnit constants:
ActivePresentation.Slides(1).Shapes(1).Chart.Axes(1).MajorUnitScale = xlDays