I have certainly been caught out,though that is not quite what I mean. Ebay are good at informing you an item has been despatched when it actually has not and this is normally with a business seller as he removes the item from his Ebay stock and Ebay automatically register it and consequently send the email.
As for the email with a courier tracking number again the retailer has arranged delivery with the courier company and again the item is deducted from stock and again an automatic email is sent out.
As an ex courier I have a rough idea of working hours and if I get an email on late Saturday or a Sunday then I know that actually the courier will not pick the item up until Monday which means it is Tuesday delivery.
But I think generally the working day is classed as Monday to Friday even if as you say they may well work 7 days.
I know that if I need to claim a non delivery of an item by Royal Mail I have to wait 15 working days which is and that is Monday to Friday, which is odd seeing as they deliver 6 days a week.