My wife had her CFO seminar on 28th of May. That was the only available spot when we looked to book an appointment on the 25th when we picked up her passport. She got to the office at 6am and was one of the first in line and since she was early they actually did her interview before the seminar instead of after, she had no issues getting the certificate as it was emailed before she left the building.
I know others had issues some issues, but I recommend get there as early as possible and be one of the first to get interviewed. Those counselors see hundreds of people a day, so I am sure they get more and more aggravated as they go through the day.
So my advice, book when visa is on hand and go early, yes you will wait awhile but rather wait for hopefully an easier process than being the 200th person interviewed. Also, make sure to bring all the documents as requested on the CFO website, we just brought the entire packet she had for the interview.
Hope this helps!