I run an average of 18-20 hours on a full brisket with indirect heat at 225. If you have a more direct heat source it may take as little as 8 hours to finish your brisket. The best bet is to get yourself a Polder thermometer. This way you can track the internal temp of your product and then you will know exactly when you hit your plateau and at what temperature the conversion process began. Once your temperature starts to drop you know you have begun that process. I often find that happens at around 170 or after about 8 hours on my ceramic cooker. The longer you can extend the process where collagen is converted to gelatin the better your end product will be. In short don't rush it. A Polder thermometer is a solid inverstment and the good news is that they are not expensive. $30-40 buys a nice one.