I think they just use that expression to make it clear they'd expect you to be there at 5. Last time the queue went from the front door and snaked round an alley at the back, but the only ones taken through a side door were those with priority tickets (which they didn't offer this time). Might even be to try and ensure people don't star queuing too soon, as that can make the police in Oxford Street twitchy.
Last time few in the store knew much about the arrangements as HMV sent a goon from their PR department with all the gentle manners of a stormtrooper, accompanied by a security force just short of being armed with weapons to manage it
