How do I get the mapped value of a datetime (or string) on an axis in the FillSceneGraph event?

I've done this for scatter charts where the axis is a number, but when I try do the same thing for an axis that is a DateTime or string it gives me some crazy value. Here is what I did:

IAdvanceAxis

xAxis = (IAdvanceAxis)e.Grid["X"];

int

x1 = (int) xAxis.Map("02:00"); // Gives a crazy value that is way off scale

int x2 = (int)xAxis.Map("Monday"); // Gives format error