That seems reasonably long. I think the other aspect to determine is who is going to interview you. I've heard, but I'm not too familiar with female interviewing dynamics, that females can be competitive of each other. From a male perspective, I don't think your nails will make your break you as long as they don't make that clacking noise on a clipboard/briefcase or whatever prop you choose to bring with you to your interview.
You can always dress to impress, but I think being conservative and plain as vanilla will be best since you want to play the odds. Pretty much go in there and be able to impress as many people as possible while reducing all variables that anyone may deem negative or inappropriate. Once you dress the part, the more important part is to play the part. That is what will seal the deal.