Sounds difficult to appeal against considering there are no records ie. recording or video-ing of the exam, and the exam board would usually trust the examinator to deliver sound judgement; I have not much idea how to go about repealing the judgement, although perhaps if they deign this particular examination to be unfair, you may have a chance of a repeat performance, but then again I have no idea of their policy as I'm with a different examboard. Sounds incredibly dogmatic though to remark about your tempo, rhythm I'd say is fundamental, whereas timing is relative. Goodd luck with the appeal.