No worries MiggHD, I think the application window is usually open for a couple of months, I guess that may depend on how many applicants they get though. I am confident it will still be open by the end of August. However have you asked CTC if you can apply before you get your results and input them later?
As for your stammer, I don't know whether this would affect you or not. You could try contacting Dr Peter Orton at Aviation Medica, Stansted Airport - I saw that you're in the UK. He's the only person in the UK (and possibly Europe?) to certify a QCAA Class 1 Medical. Maybe try calling them and see what they about your stammer - it may be that they can't make that decision, but I am sure they could offer you better advice than most people on here (me included)
They're easily found on google