Thanks for your patience. I'm learning more about Visual Builder as I go here...
If you have your first aggregation which is a Filter Ratio which is calculating success/(success or failure).
That ratio probably changes over time, and your gauge or markdown is showing the last value. But it sounds like you want a metric that shows the percentage over the entire timespan, which might be Last 15 minutes or Last 30 days.
So you can add Overall Average aggregation to do that. First click the + sign on your existing aggregation, and then select Overall Average under the Sibling Pipeline Aggregations.
The Metric field to the right, should list your Filter Ratio aggregation from above (mine is different in this screenshot);
So now you shouldn't have to worry about the Interval and it should just be set to Auto.
Let me know how that works.