With IETour, the stage layout with the long catwalk down to e-stage meant there was plenty of rail space to go round. At the first London show, I arrived to the queue at maybe 12.30pm, was about number 300 in the queue and got to be right by the rail near e-stage. A friend who had arrived at 9am got to be right on the rail.
With this stage lay-out, it doesn't look like there will be so much rail space, so I would advise getting there as early as you can. Officially, some venues might tell you that you can only queue up outside from 9am or something like that. If you can't be there all day,