Bad news, it's not arriving today like I thought. The delivery was delayed because the order was taking a payment via direct debit. Spoke to someone at AAISP and I've now sent AAISP a separate payment via bank transfer instead which I'm told will also cancel the pending direct debit payment.
I was also initially told that due to high demand there will be a delay on shipping, but since then I've now been told that once they see the manual payment I sent to their bank account some moments ago then it should be despatched later today for delivery tomorrow. One thing still slightly puzzles me, it says Royal Mail Tracked 48 (not 24?) and that is what I've now paid for, so perhaps they'll just do 24 anyway given the unfortunate misunderstanding with the order. It's all becoming slightly more confusing than it should've been.
Fingers crossed it arrives tomorrow!
EDIT: Got a tracking number now, I don't know if it's 24 or 48 hours though so I'll find out soon enough. If it's actually 48 hours then it will most likely turn up Monday or Tuesday of next week (sigh), but if it's 24 hours then it should arrive tomorrow (hopes!).
EDIT: It's Royal Mail Tracked 24, woohoo! Just waiting to see Royal Mail's tracking say that they have it, at the moment it still says "item expected".