I have one year left at uni, when is the best time to apply to join afterwards?

If you only have one year left then i'd advise to start the application process now - whether you are looking to join as a soldier or officer. The great thing about the army (both as a soldier or officer) is that once you pass the selection you can choose (within reason) when you want to start. Many people apply and pass the selection whilst at uni / college as they then know (when they've finished) they have a guaranteed job and can start at a time that's suitable for them (people sometimes travel before hand or take up another job somewhere etc). Good luck.