Gantt labels may be configured in Schedule tab > Gantt tab > top left dropdown > Configure Global Display Options.
Steps to create a custom blast label.
To organise Gantt labels:
Select ‘Configure Global Display Options’ from the view switcher.
Add four labels to the Labels tab:
Label Above
Label Inside
Label Below
Tooltip
In the Label Above group, choose what to show above delays, blasts, drills, stockpiles, and so on (for example: hours, kilograms, meters, and tonnes).
Repeat for Label Inside, Label Below, and Tooltip.
Press the gear icon to add custom labels, such as multi-line tooltips or concatenated labels.