As part of this metabolic style of eating, you can take one day a week where you eat what you want. The metabolic strength the diet gives you means you are less likely to put on fat when you stray from the plan.
I recommend that you leave this day rolling until you actually need it. An inpromptu work gig on a Thursday or a christening on a Saturday are both events you want to be able to enjoy. Its lost on you though if you set your cheat day for Sunday, as the day may come and you might not even feel like eating diifferently. Save it for the times when you know sticking to a meal plan will be difficult.
Enjoy yourself, but dont go overboard. This is not an excuse to over indulge, just enjoy life and the foods you like. Go to a cafe, order what you want and get a dessert, dont go home with a chipper, a can of coke and a snickers. This would be a set back, not a perk.
So be responsible, but enjoy your life.