Code snippet to set the first chart on a wordsheet ($ws) x-axis to a date/time type and set the major unit to 500 and minor unit to 1 – useful when dealing with long data setup where the general/text type requires a greater than 255 manual separation value.

$chart=$ws.chartobjects(1).chart 
$chart.Axes(1).CategoryType = 3
$chart.Axes(1).MajorUnitScale = 0
$chart.Axes(1).MinorUnitScale = 0
$chart.Axes(1).MajorUnit = 500
$chart.Axes(1).MinorUnit = 1