Not sure if this helps,
but about a year or two ago i queued up for a jeremy kyle book signing with my grandma (dont judge me i was just escorting her)
anyways, the arndale staff have a set procedure for high profile events (assuming it will be the same for the iPad launch).
The doors to the arndale open earlier than the stores anyway (due to the indoor markets that sell handbags, phone accessories etc, some of you will be familiar with this) so the waiting for the arndale to open before the apple shop will not be a problem.
Then the outside of the apple store will be supervised by arndale staff with a barrier set up to ensure people form an orderly queue (this is what they did at the book signing anyway).
From memory the doors arndale open at the same time as the foodcourt, from memory thats about 7ish. although the shops dont open till 9am, the apple shop may open at 8am that day though, although, as i used to work in the tesco on market street, the shops in manchester are obliged by law to only trade at specified times, so not sure apple would be able to open earlier without special permission, which they probably have.
Anyway, feel free to ask me anything i havent covered here, ill do my best to help
