Remove used options: options still visible

I try to achieve the same thing as Mark in this thread: clients can pick a time slot from a list of available times (radio bullets).

So I made the field unique and that works, because once a time is selected by someone, it cannot be selected again (when you submit the form, you'll receive an error that the time is not available anymore).

I would like the non-available times to be hidden/removed from the list. So I used the Code Snippets plugin and saved+activated this code. I replaced the field codes in line 3 (100,101,102) with the field code with the times in my form.

However, it doesn't work. All times remain visible, including the times that aren't available anymore.

Can someone please give me a pointer as to what I may have done wrong? I appreciate any help!