The boxes are scooped in the morning and in the evening. I never scoop in between. if it is particularly stinky it usually means it is not covered. I shift the litter so it is. Usually works. (hee hee)
We have 18 boxes. I use scoopable litter but really don't dump it as often as most people.
A round of scooping probably only takes about 5 to 10 minutes depending on whether I need to add litter to the boxes or not. But when it comes time to scrub the boxes, it is a big chore. (lots of stair climbing).