I think you have already tried the VB6 sample code, which includes a real time chart example. In that example, the data arrays are filled from the right to left. In your chart, you can always fill the data arrays from left to right instead, that is, the first data point is stored at index 0, the second at index 1, etc..
If your timer interval is 1 sec and you want to display 30 minutes of data, you can set the sample size to 1801. In your code, you can stop filling the data arrays when it is full.
I have attached a modified "frmRealTimeDemo.frm" example for your reference. You can use this file to replace the original frmRealTimeDemo.frm in the sample code. This modified example plots the chart from left to right, with 1 second per data point, and stops after 1801 points. The chart only starts only when you press the "Start" button.