[K Dubious]

Yeah your dates are a little off...

Also it could be guaranteed to be sent by that date and not necessarily guaranteed to arrive by that date.

I'm fairly sure this is an arbitrary date created by the parameters that were given when the listing was created (like handling time and type of shipping) which is not always accurate due to the way ebay automatically checks certain boxes based on listing details.

Lastly I do not think that guarantee is worth anything, no one can guarantee an item will arrive as shipped and could be lost in the mail and that's why there is shipping insurance. Ebay wouldn't cover anything like that.