I suspect Asda could be considered a grocery shop ;-)
Not so sure about "quite right too". Unless earlier slots were available and rejected by the customer, that is. After all, it's the shop who chooses to offer available delivery slots rather than the customer insisting it must be a fortnight away, after the offer period. So in that case it ought to be when they accept the offer to purchase that counts, not when they get around to delivering the goods and taking the money.