They'll ask you to put in your info and youre in queue from that point. I believe most ppl spend time within the department store until they're called. Some days you won't be able to get in unless you participate in the running in the morning, some days you may get lucky and get in even if you show up at like 11am to put your name in the queue.
I've heard non-department stores such as Dosan and Shilla are easier to get into, not sure if ppl line up at those before opening.
As for prespend, Korea is pretty rough, I've seen numbers upwards of 5:1 on some Korean bag forums