You seem to be getting a lot of wrong information.
Our software jailbreak does not effect your warranty.
There is no chance for a software only jail break of 5.8.10
Amazon chat is wrong and they usually are about very technical aspects of the firmware.
No, the thread you linked to has never been maintained by the author.
You can see by the edit date of a year ago last August.
The only one that is current for your device is:
https://www.mobileread.com/forums/sh...d.php?t=275877
And you must take up that option to return your current device within the two weeks that you mentioned in order to get one with old enough firmware to jail break.
Waiting around until you "get the time" is not an option.