Thi cannot be done using a date picker, as this is linked with a single attribute, which can only store a single date. Just like you can only enter a single date in a single cell of an excel sheet. ( if you achieve more, then it is a string and not a date ;-) )

Solution is to add a extra entity “Date” to your domain model and a option in the page to add a extra date in your appointment. Each time creating a new Date Object