Hold in there mponse, I think they may be doing it in order of application. I applied and had the questions in within the first 3 days of the opening date. I have subsequently been given an assessment for the very first day. I think they may want to give everyone equal time between invitation and assessment day.
For example, I have little more than a week to prepare, whereas to give somebody who isn't down to be assessed until the very last day of the process (3 weeks away) an invitation now wouldn't be fair, as they would have over 3 weeks to prepare for it whereas I only have 1 week to prepare.
I hope that makes sense