If you push hard enough you can get an appointment on the day, I got an appt a couple hours after booking.
I had an interesting experience with DSM on launch day.
After being told, time and time again, that no watches would be available in stores and that we must abide by Apple's queuing system of ordering online (which I actually think was entirely fair and the best way to manage both the demand and supply), DSM quietly announced the day before launch that they would have a small amount of watches on the day.
But they werent accepting any queues, they would announce a dedicated number in the morning and you could make first-come, first-served appointments.
So in the morning about 7am I had a look for the number, but it wasnt there. I checked again at various intervals and eventually (nearly 11am) the number was there. I rang it and got a call failed tone, so thought the line hadnt launched, but it had. Rather than have a line busy tone or message, let alone an call waiting queue (which would have been much more fair), if you tried to call and the line was in use which was all the time - it would just cancel as if it failed. It was a disaster.
Some people, it turned out, sat and dialled and re-dialled on repeat over 700 times before getting through, only to make an appointment for a weeks time, with no guarantee of stock.
Anyway, I tried again at 4pm and actually got got through, only to be told there were no appointments, the phone line was now out of use and I had to go to the shop on the Monday, to book an appointment for the following week despite the fact theyd probably be out of stock. I pushed the person on the phone to see if they would budge. I told them I didnt need a try-on appointment, I just wanted to hand over my money, so whats the point of physically going there, just to make an appointment it would take more time. But I was repeatedly told no.
But feeling curious, at 5pm after work I made the trip over to DSM (its not far). I walked in, headed to the table where a couple of people were looking at the watches, some having appointments. Someone came up to me right away, asked if they could help. I asked if they had the 42 SGS in stock and he said sure, took me to the till and 2 mins later, I had my watch on launch day, no queue, no appointment.
In front of me at the till was a guy that had stood outside since 4am, only to be told to call the number and make an appointment. He had called 400 times and been given a 5pm slot.
Behind me in the queue were two guys that had flown in from Italy and managed to get an appointment also.
Neither were very happy about me being there.
I say this just to show that it's always worth a shot and don't believe their "rules" that are really only there to stop manic queuing.