No. Once you print the label it is a done deal (the ship date is printed on the label)
This has never come up here in discussion to my knowledge.
"Stale" label issues have arisen where the date on the label is Tuesday but it gets shipped late on Thursday, and an overzealous postal worker raises a stink, but the opposite situation has not (that I am aware of).
I don't think it will be a problem. Just ship it (and don't make an issue about the date if you take it to the PO counter giving an overzealous USPS clerk an opportunity to make it a problem when it is not).
Now that I think about it, I think I did one a few months ago. Created label with a Tuesday ship date (can't recall why), dumped it in mailbox and it was picked up Monday (a day early). No issues, tracked just fine, and was delivered just fine.
I scrutinized the DMM, and it appears to technically say that the date must be correct, and that mailers CAN and should make a single mailing date change to the label if not mailed on the printed mailing date, BUT, I read it correctly, the entire indicium has to be added, new date, new 2d postage barcode with encoded additional $0.00 postage, etc. Same idea as those $0.00 postage labels USPS sometimes slaps on at the counter such as when remailing a package returned due to USPS error.
It is not possible for you to do that using eBay or PayPal provided mailing labels (that capability is for mailers with their own postage systems with a provision for that in house.
A USPS clerk should be able to generate and apply a $0.00 postage label with the correct mailing date as the postage is already paid, but I wouldn't go there unless you want to experiment.
Just mail it and you should be fine.
