I, normally, use 'from what time' and 'how long' to ask someone (e.g. a seller) something like
from what time did you open the store, today? How long is your shop is open today?
But I don't know if 'from what time' is usual or no. I think that 'since when' is sometimes used when I have a complaint and say for example
Since when did you have the right to get my father's book?
Tell me please if 'from what time' is a usual phrase to ask such things.