Why no hours option for tasks in Premium edition?

I upgraded to the Premium level of Zoho projects, thinking that I would be able to create task durations using hours. After all, the feature grid said I would get a "Business Hours" feature. However, once I started using it, I found that there was no hours option, and only whole-day increments were allowed in the Gantt view.

I get the same message if I try to put fractional days into the detail window. What is the use of "Business Hours" configuration if the program completely ignores all hours information? Why would the developers exclude such a basic feature from Premium?