After the first slot completely closes (current time passes closing time), the next one opens up:
Both preceding slots are pseudo-full, and therefore the 3rd slot opens.
After a few people enque it looks like this:
Note that if the last slot in the sliding window is full, it still works as intended
I am open to suggestions on how to phrase the parameters for the end-users. Currently it is horrible.
Closes #575 (closed)