Does a Buyer have the right to complain if item is not posted within 3mins of them paying for it?

[millyswardrobe5]

Last Friday on my way home from work I recieved a payment from a buyer at 4:57pm.  At my location the post office closes at 5:00pm and I didn't have enough time to post it.  So the very next day being Saturday I lodged the item at the post office.  Since the post doesn't go on , Saturday, I explained to the buyer that it had been lodged and will be posted on Tuesday as the Monday was Australia Day Public Holiday. I also gave the buyer the tracking details so they could see it had been lodged and track the parcel if need be.  Today I received a sarcastic message saying that they haven't received their item and if I had posted it on Friday.  I am in the wrong?  Is it an unrealistic expecation to pay for an item at close of post time and expect for it to be posted.  Please note that it can take me 15 mins to drive, park and walk to the post office. I'm not sure if it was of great urgance that the buyer recieved the item earlier, they did not indicate or tell me they needed express post.  My description stated that it was standard parcel post.  I also had a buy it now option so the buyer didn't have to wait for the auction to end.

Can they leave negative feedback becuase item was not posted at the same time it was paid for?  I also stated that I would try and post items within 24 hours of receiving payment.  Which I have done.