Questions about the hiring process

A little over three months ago I attended a recruitment event for asst. conductor trainee positions. I passed the tests and thought the preliminary interview went well. We'd been told at the beginning of the event that we'd hear back about the next step in the process within three weeks, max. At that stage, we'd be given materials to study over a five month period before taking an exam and being interviewed by a panel of people. It's been over three months since that recruitment and I just today got an email about scheduling a two hour "trainee assessment". This wasn't mentioned at the original meeting. Since what I was told so far has been inaccurate, what should I actually expect? I'm interested in the job but going to this assessment would require me to miss part of a day at the place I just started at. Given that, if someone who works there could share some insight into the process of getting hired, I'd really appreciate it.