Sorry, but this cannot be done with an YX_Chart.
In YX_Charts, the X axis values are doubles and are treated as numeric values.
It can be made with a LINE chart and MissingDataValues.
You need to use xChart1.AddLineMultiplePoints.
When you have missing data set its value to xChart1.AddLineMultiplePoints.
Attached a modified version of your project.
I used -1 for the MissingDataValue, up to you to set any value you want.
I removed the xChart properties settings to the Designer.
On the first time stamp there is no value in the red line, the line begins on the second time stamp.
On the second time stamp there is no value in the other line, no circle drawn at the second time stamp.