Interview for a part-time job (3-4 hours) – what does it involve?

Hello,

I have a retail interview on Thursday morning. The woman told me to plan on 3-4 hours. I'm just surprised, since it's an 18-hour-per-week position (Mon-Sat), so why should the interview last 3-4 hours? She also didn't mention anything about a trial period, just an interview.

Do I need to prepare for anything? I've never seen anyone interview for a part-time job that takes three or four hours.

Thanks.