It depends on your level of insulin resistance and and how fast you wish to lose weight. To be honest, with all the delicious food you will be eating, every day will feel like a cheat day. The key here is preparation. Be sure to have everything you need on hand and know where to eat out where you can enjoy banting-friendly food.
The problem with cheating is that once your body has used up all its glycogen stores and become fat adapted, your body creates ketones to burn fat. If you cheat, your body begins burning carbs again rather than fat and you stop losing weight. You then have to go through the cold turkey all over again.
For further information about how ketosis works have a look here.