The group work is all in the morning so its down to when youre scheduled for your afternoon interview. Mine was the last of the day finishing around 5.30 but the first lot were done by around 1. If you need to get off early it might be worth asking if its possible to have an earlier slot.
As for the techinical side I think they want to see more of an ability to figure things out and reason rather than an all out knowledge. If you have no flying experience make sure you read up on the principles of flight and the partner airlines. Its no more difficult than that