I booked the NCT and they allocate you a class on due date. I think mine was 6 weeks prior. I had them extremely prematurely and my babies were about 8 weeks old by then. I booked it primarily to make friends with kids the same age as I'm quite quiet and now I know no one. Surely if they held them earlier some of us who have premmies will still get included? No idea why they are so last minute!