I've never ever had a package returned if I had the incorrect date on it - say, I printed the label out Saturday night and neglected to change the mail date to Monday. Especially if the rate is unchanged. You could drop it off a week later, but really, as the shipper/seller, you're only doing yourself a disservice as that becomes an INR (Item Not Recieved - at leas on eBay).
The DelConf tracking (which isn't tracking ;) ) would show the Electronic Info was received on Saturday night.
However, the next time the package got scanned could be at the P&DO or even regional center. Technically, there is NO obligation on the part of the USPS to scan the item other than at delivery.
However, luckily for us, they do seem to doing it on a much more frequent basis, so you can, in fact, "track" the package