my assumptions and explanation of the whole story go like this:
many people pre-ordered for 24.99GBP on 29/10 when it was live by mistake for a few hours, then it went officially live yesterday, and everybody that already had an order in re-ordered for the cheaper price and then cancelled the old order.
so: zavvi "sold out" within 25 minutes, then said there was a "glitch" (when in fact they just received hundreds of cancellations of the 29/10 orders) and then made the cancelled orders available again, this time immediately, which is unusual, but given the supposedly high number of cancellations they received and the immediate sell-out it probably made sense.
i am confident that even people who ordered after 6pm. UK time will be safe with their orders.
what's more, we don't even know the exact print-run. zavvi only said "1000 available", but that doesn't necessarily mean that's the print run. probably they stated what's left (after the 29/10 orders), when in fact it could be a 2K print run (with 1000 available yesterday before the cancellations).