I closed for a week at xmas and still charged for the days off. If parents are going to make a big deal about 4 hours, then maybe next time you should just take the whole day off. Your health comes first. A lady in my area just recently closed because of health reasons. You are already open 11 hours per day, don't let parents take advantage of you and take care of yourself. Also, if you tell them you have an appointment at the hospital, I'm sure they are not going to demand a discount and be understanding.