Can Numbers use 8 hour long days when converting from days to hours

Using Numbers 3.6.2, I am using cells formatted as "Duration" in days. I then have a SUM cell that sums all the durations and shows for example "64d" (Suppose in cell D1).
I then do in a new cell (D2 for example) the following formula: =D1 and change the display days to hours. It shows "1536h".

But I want to use days of 8h (a normal average working day). How can I do this?

If I change the formula to =D1*8, then I get 8 times as many days which is certainly not what I want.