It's not much consolation, I know, but AP guarantee that as long as both the sender and the recipient of Express Post items live in specified Express Post areas (as detailed on the backs of their envelopes/satchels), the item will be delivered the very next working day, and if for some reason it isn't, they will provide you with a replacement envelope/satchel of exactly the same type at no cost.

I don't use Express Post very often these days but there was a time a couple of years back that they were almost always delivered the very next day, even to WA from Brisbane, but lately this has simply not been the case, yet in every instance where AP failed to deliver the next day, as per their promise, I provided them with the peel-off sticker they give you upon lodgement and within a few days I received a replacement envelope or satchel in the mail by way of compensation.

As I said, it's not much consolation when when you consider the degree of inconvenience that has been caused in many cases, but given the exorbitant cost of Express Post these days, reimbursing you for the cost of the postage is the very least they can do under the circumstances. Just make sure you don't lose the peel-off sticker when you lodge your article and you'll be covered under AP's (almost worthless) "next-day" guarantee.