Hello Clare,
You should be able to format the Data Labels is you specify <label> for the Data Label Format field. You will then have to use an expression for the format in the Value Grouping Editor -> General -> Data Point Values -> Label field.

Best Regards,
Nevron Support Team

I currently have a bar chart and each bar indicates a length of time in seconds. Currently the label that gets displayed on each bar is just a numeric value in seconds.  How can i get this to display in hh:mm.

I tried changing the label in the data values grouping editor, but its still showing the value as a number only.