This is variable, I use the 9012DC at home, I am fortunate in that I test new ideas so I have a custom double height cup that was made by gluing two cups together after sawing off the base of one and the top lip of the other. Even this cup though I can fill in a day if I wet skim while carbon dosing which I do time to time if a test shows higher NO3 and PO4 but if I am skimming with a normal setting with the pump turned down to where I get a more dark iced tea then I get a week or so and the cup is filled to the normal height of a regular size cup. My general experience is that you don't really want to go much more than 5 days between cleaning the cup, as even if the cup is not full, the crud caked up in the tube starts to reduce how well the skimmer works. If you want to go longer, the holiday cup 9012.145 was what we made instead of the double heigh cup and it drains to a bucket, if you skim wet, the cake up of crud in the riser tube is much slower so then you can go longer between cleaning.
