Different types of cleansing, require different time periods.
Products like Colonix, use herbs that bulk up and latches onto any fecal matter inside your colon. This is debated if it even works, but nonetheless, it will take much longer for products like this to work effectively. That's why they recommend 3 months.
There are other colon cleansing products like Oxypowder that use oxygen to melt the fecal matter inside your colon. This is one product that is highly respected in the colon cleansing world (like Colonix), but you only need 7 days to clean out the colon. And it will clean it out effectively.
Then you have different processes like Hydrotherapy, where you will get you colon cleansed thoroughly in about an hour. Of course, many people opt out of this, because it's quite invasive. I don't find it that bad. More embarrassing,then uncomfortable.