I think it's important to call the clinic and ask before you start treating your yeast infection. Since Monistat 1 is a single treatment, I would think that you'd be fine to use it today or tomorrow. But, you should call the clinic and let them know. You don't want to get there on the 26th and find out that they can't do the MA right then because you have had a recent yeast infection, or have used the medication.