Visa application centre turnaround time

[venusloon]

I'm in a pickle!  I waited way too long to do my student visa application to study in Belfast.  I have an appointment this Wednesday (6/18) at the visa application centre, but I'm leaving for a two month vacation to New Zealand two Saturdays from now (6/28).  My dilemma is that since I have to mail in my passport and other documentation to NY after my appointment, I'm really afraid I wont get my passport back in time to travel.  That effectively gives them 6 business days to get my passport back to me if I/they overnight the package.  Is this likely?  I do have time between when I get back from vacation (9/2) and when classes start in Belfy (9/29), so I can put it off until then.  Will they get pissy that I applied so close to the entry date?

Thanks in advance!

EDIT:  I'm going to go the courier route to expedite the processing.  I'll let you know how it turns out.  Thanks everyone!