I'm in the same position. Still not even processed payment, so they must be very confident that they'll be able to fulfil these orders in time for Monday.
I'm not optimistic though, as this is a carbon copy of the situation I was in last year for the Star Wars blu-ray release. I pre-ordered in January for release in September, and they only began shipping on the Saturday prior to launch. I didn't receive my copy until the following week, despite assurances that first class postage would guarantee release date delivery.
Mine is still on awaiting dispatch. If it turns up late and you paid for release day delivery, as has happened to me before if you email Amazon Customer Services they will apologise and refund the postage but I still have my fingers crossed. Given the high cost of the set they will probably courier them anyway.
You've got me a bit worried now. I pre-ordered this on 11th January, added 1st class post option a few months ago, and mine still says not yet dispatched. I've never pre-ordered on Amazon before, is this usually a problem?
Edit: it still says you can get next day delivery up to 7pm on Sunday.
Had this ordered since early September. Still hadn't dispatched Saturday evening despite me paying extra for delivery. Get an e-mail Saturday night saying there's a problem with my card (which there isn't, I double checked). Poor show Amazon.
I emailed customer service. Was told there was a problem with the dispatch process that may take 48 hours to sort, so cancelled. Asda will be selling it for £87.97 I think. I love Amazon usually, but I wont pre-order again!
For the record, pre-ordered on standard with 1st class. Despatched the Sunday (day before) before release, came Parcel Force on the Monday. Only way I could have faulted them was for making me wonder if I'd get it!