I'd include a carb refeed whenever you feel like it. It doesn't matter if you are deep in ketosis, or just slightly. The point is to keep carb refeeds sporadic. If your body gets overly used to a pattern, it will adjust and the method will be less effective. Eat ketogenically most of the time, but randomly toss in fasts and carb refeeds to keep it guessing every now and then to prevent your body from fully adjusting to a pattern which might actually SLOW your fat loss.