I just spoke with Virgin Atlantic on the US side and I have some good news for people. Many people believe that you can only book your pet's flights two weeks ahead of time. NOT TRUE!
I just booked both my dogs on a November 13th flight out of Boston. I will book my ticket once I have my visa and will book it for the same flight. If I can't get a ticket on that date, I can call the Pet Area and have them move my dogs to the flight I could get.
THIS DOESN'T COST YOU ANYTHING!!! It is free to book as you pay on the day of departure. It also allows you to change your pets departure date much more easily because you already have them booked.
I hope that this helps some people out! Happy Flying!