Divide by 12 to get the SHAH ZEMANIYOS
The way we learned in fifth grade, is that you take the number of normal hours in the day and multiply by 5 to get ???? ??????.
For example, if sunrise is 7:30, and sunset is 4:00, then there are 8.5 hours in the day. Then, 8.5×5=42.5, so there are 42.5 minutes in a shaa zmania.
(Ok fine, we learned it like you, but then I raised my hand and said we could just do it this way. And the rebbi agreed, after we tried a few examples.)