All the 9/18's I've seen are radials, so I assume it won't require reversing them (which a tangetial extractor would), but the main test is to watch how much honey flows out. That's the real test. On a hot day this will happen faster. If the supers have had time to warm up inside it will happen faster. If the supers are in a cool room it will happen slower. If you harvest on a cold night and try to extract the next day they may still be cold and it will happen slower. You get the idea. If the honey is drier (lower moisture) it will happen slower.
The point is there is no set rule because temperature and moisture change everything dramatically, what you want to look for is that most of the honey had come out of the combs before you really crank it up. It takes a bit of practice and paying attention at first, but it's easy once you get the hang of it. The first batch is the one to pay the most attention to so you get the idea of how fast it's coming out of the combs. You may have to run that first batch on slow for a little while and look at them. Lift one frame and feel how heavy it is. This should give you an idea of how fast it's coming out. If you are gentle you can extract thin surplus or foundationless frames with no wire. If you're impatient you can even blow up combs on plastic foundation or wired wax. If you blow out some combs, you won't be the first beekeeper to do so. :) It will wake you up!