I don't suppose there's any way you could raise your potential problem with your potential employer, and ask if it might be possible to have an interview out of office hours? Just outline your problem with them as you have here. The worst they can do is say no, then you may have to take a Plan B, but if I were a potential employer I'd be impressed by your honesty and reluctance to 'take a sickie'. I could be living in dreamland, of course, but it might be worth thinking about?