most schools are receptive to date changes, but remember that you are already interviewing late in the game. Competition for spots is going way up. I find it difficult that your employer is not receptive to the fact that medschool interviews are pretty hard to come by. I think you would be better this late in the game trying harder to get out of whatever thing this that you can't miss. Every day that goes by, your chances of getting in are reduced. Now if this school is way down on your totem pole and you already have an acceptance to go somewhere else, it is a totally different story.