How do I display the start of a query interval on a graph time axis?

When creating graphs in Grafana, the window size and time range create a query interval used for grouping data points and applying a function to select from them. This is seen here:


My data is aligned to 15-minute intervals (XX:00:00, XX:15:00, XX:30:00, XX:45:00), but because the query window is 30 seconds, the graph shows the data at end of the query interval (XX:00:30, XX:15:30, XX:30:30, XX:45:30).

I want the graph to display the start of the query interval, so data averaged from the window XX:00:00 to XX:00:30 is displayed at XX:00:00 rather than at XX:00:30.

How do I change Grafana settings so it shows the start of the interval window?