Someone who actually knows will correct me if I am wrong but I think your ATPL exams are valid for 7 years after the last one is complete provided you keep your IR current?
On a brighter note bunnyhop the best thing to do when you finish is to try and stay in aviation and keep current, think about an FI rating provided there is a job etc. It's a scary time for low houred wannabes and will continue to be for some time yet.
It's going to be a long hard road mate, be prepared.