Scheduling Conflicts

I've been working on scheduling my defense for almost two weeks. It is impossible. I was closing in on a date when the one person who didn't respond to my emails for over a week decided to write back and throw a spanner in the works and say they can't make it. So, I got to start all over from scratch. Let's bear in mind that I am already pushing the deadline, and nobody replies during winter break even when they haven't gone anywhere, its like this entitlement thing. Okay, I will quit whining now, but geez, at this rate I have to wonder how they EVER schedule faculty meetings?