How do you assign hours per week for use in dashboards?

I want Asana to display charts based on Estimated Time using 40 hrs/week. It currently thinks a week is 24*7. For example, 1040 hours should ideally be 26 wks, but it shows up as 6 wks effort. Any way to set this?

Where does it show up like this?
You are using tasks with start and end dates?

It shows up in the dashboards that way. I have charts plotted based on Estimated Time as an axis. When it shows the number of weeks, that is calculated with 24*7 hours a week rather than 40 hrs/week that I want.