To show DateTime related values on the XAxis you can choose to set the XValueType
property.
In your case Series[0].XValueType = ChartValueType.Time
would be the right thing to display time related values.
To format the values you can use ChartAreas[0].AxisX.LabelStyle.Format
which would translate your values into the required format say like HH:mm:ss
.
ChartAreas[0].AxisX.LabelStyle.Format ="HH:mm:ss";