Unfortunately, there doesn't seem to be a way to suppress just the hours and minutes information from the chart. You can remove the 'Duration' label itself, but in turn you would lose the 'Days' label along with the 'Hours' and 'Minutes' labels. Since the Gantt chart is dependent on a specific span of time, the hours and minutes are a part of the component and how that information is displayed.
That being said, I would encourage you to input an enhancement request using the link below:
Doing this helps us in determining which features can be added to the product in the future.
I raised an enhancement request for this.