At some schools it means that you'll be a non-tt Instructor until you finish your Ph.D. You need to get clarity on exactly what they mean by that.
No, you don't.
To understand why, you need to consider how the question sounds to a search committee:
What a candidate says: "Exactly what does 'PhD by date of appointment' mean?"
What an SC hears: "Um, I'm not nearly as far along on this diss as my letters indicated, and I have no idea when I'll actually be ready to defend. Just how long can I stretch this thing out?"
For now, don't worry about it, and instead focus on writing. If you get an on-campus interview, the department chair will explain the details of the deadlines to you (and the consequences of missing them). You will thank her for the information, but not appear too concerned about it. At some point in the course of the conversation, you will have the opportunity to reiterate that you will be defending long before the next academic year begins. The department chair will be inwardly skeptical and wonder why you don't have a date set yet, but at least you won't be sending out "I have no clue when I'll finish" vibes.