From what you shared it looks like you stored everything in the same entity. You should expand your domain model with adding an entity Date, add an association with the Interview entity. Then you can have several Interviews added to the same Date that is stored in the new entity.
So when you save an interview you need to make a find-or-create action. You will make a retrieve from database with a constraint on the selected date (you will look if the selected date is already in the database). If it is in the database already you will add the interview object to this retrieved date, if it's not you will create a new one.