Jordiejet,
got the invite yesterday, I applied the Wednesday before the Friday deadline, so I think its fair to say that they are very busy and you should not worry if you have not heard yet.
On the assessment dates - January dates were available yesterday. I waited till this morning so that I made a suitable choice and there were only Feb dates to take. I guess my advice is when you do get an invite- don't delay.
Best of luck mate.