I think the problem is that the length of time varies depending on the source of the animals. I recently ordered some clean up crew that came from a dealer who held them in a fishless system. I just gave them a rinse in a bucket of clean tank water, and in they went. On the other extreme, I was at a LFS last month to buy some CUC and they had a tang with ich in the same system, I didn't buy anything of course....the risk would have been too great.
For invertebrates of unknown history, holding them for 45 days in a fishless system is almost always going to work. 30 days would be my minimum, simply due to the fact that Neobenedenia fluke eggs are sticky and can be carried along with inverts, and they take that long to hatch.