Here's how you do it, as copied directly from Pounds and Inches:
Unforeseen Interruptions of Treatment
If an interruption of treatment lasting more than four days is necessary, the patient must increase his diet to at least 800 Calories by adding meat, eggs, cheese, and milk to his diet after the third day, as otherwise he will find himself so hungry and weak that he is unable to go about his usual occupation. If the interval lasts less than two weeks the patient can directly resume injections and the 500-Calorie diet, but if the interruption lasts longer he must again eat normally until he has had his third injection.
When a patient knows beforehand that he will have to travel and be absent for more than four days, it is always better to stop injections three days before he is due to leave so that he can have the three days of strict dieting which are necessary after the last injection at home. This saves him from the almost impossible task of having to arrange the 500 Calorie diet while en route, and he can thus enjoy a much greater dietary freedom from the day of his departure. Interruptions occurring before 20 effective injections have been given are most undesirable, because with less than that number of injections some weight is liable to be regained. After the 20th injection an unavoidable interruption is merely a loss of time.
So, the schedule if you're doing homeopathic looks like this:
Day 1 & 2: Stay with 500 calorie days.
Day 3 & 4: Increase to 800 calories.
Day 5-13: Eat "normally."
Day 14: Resume drops & 500 calorie days.
The schedule, if you're doing injections looks more like this: