I took mine into an iStore on 10 Jan (Saturday) and got it back the following Friday.
It gets couriered to the Core repair centre and back. You also have to accept the quote from the repair centre before the replacement happens. They do send emails at each step in the process, so you know where it is.
I took my phone into the iStore at Eastgate shopping center. Was told it would take 10 business days, however it only took three days. They also keep you up to date with status sms's/ emails. Just remember to book an appointment on their website or else you'll wait for ever for them to run the diagnostics and book it in.