It took a few weeks in my case. Though I'm not sure of the exact timescale because the hospital wrote to my GP but neither thought to, you know, actually write to me. So if you're anxious, you'd be advised to keep phoning up the neurology department.
They ended my test a day early too but I gave them a bucket-load of seizures to study. It seems a bit wierd them ending yours early if you didn't. Though 'weird' is only one word for it; 'downright negligent' might be another. You should ask questions about the technicalities when you get your results. And see if you can actually get a straight answer out of them. (If I sound bitter, well, I am a bit).
Good luck with your results anyway.