Hi ATC Hopeful
I did three visits prior to stage three, all very easily organised. Just phoned HR and they gave me contacts at the relevant airports/centres. Suppose it depends where your looking to book, but in my case I got to pick my own dates and times, no waiting at all.
Again it varies for spacing between stages two and three, in my case I waited two months to get a space in Glasgow for the final stage, but could have gone down to CTC the week after passing stage two if I had wanted.
Good luck though, I was in exactly the same situation with regard the personality test, failed in 2007 (because I lied) but have a conditional offer this time.