Express / Rush?

I am going to Korea next weekend to apply for my student visa, but there is some rumor mill going around that you cant use express/Rush service ？ Can anyone elaborate on that ?

Also if I deliver my application early on a monday morning, does that monday count as a working day ? as in if express is impossible now and the period is 4 days I can pick it up on thursday ?
And if express is available I can pick it up on tuesday ?