Right now the most junior CA's are from the Dec '07 time frame. They have just started getting into the '08 classes. I'm not sure how they plan on ramping up on new hires and captain upgrades. We have a way to go before we are even close to breaking even on either side. They have already downsized one CA upgrade class.
To answer your original question I think at this point you would not get offered the next class. They seem to be pretty full. When I interviewed in '07 I had to wait almost three months for a class. But there is always the possibility of someone backing out. But get started sooner so you can get better seniority