I have also been thinking the same thing, as it's very difficult now a days to even see the free slot count decrease, as it always appears that users are up all the time. It's an hour for when they need to open up the free slot. The moment you refresh the page, you will see that the 100 have already been used and added to the total number of accelerated transactions.
 
I was able to accelerate one transition just yesterday, but ever since then the rest have not been going through, and I don't think that's just a normal speed from humans, as it looks like a bot to me. The speed rate they use in using up that free slot is just a gap of 1–5 seconds, and it's abnormal to me.