How to control the X-axis timescale labels on a Dashboard 2.0 timeline chart

I've got a timeline chart on dashboard-2 that shows a running 24 hours of data. Data points are added every few minutes.

The timeline shows HH:MM over the 24 hour period. But I can't figure out how to get the x-axis labels to be "sensible". For example, the chart currently runs - 14:38, 14:56, 15:14, 15:32, 15:50, 16:08 etc. That's 18 minutes between labels.

What I'd like to see is labels every 15 minutes - 14:30, 14:45, 15:00, 15:15 etc.

Is there some way to specify this within the timeline node.

Thanks, Chris