I have roughly 30 minutes from when my office-mate leaves to my usual departure time. I love this time because I generally wrap up what I am doing, get organized for the next day, and, during NaBloPoMo, finish whatever post I've been ruminating on and typing on my phone during breaks and publish it (thank you, BlogPress app!).
Today my boss called and sucked up a chunk of that time. My lovely well thought-out but not finished post will have to wait. I know, this harshes your whole day. Stay strong!