I hate to be glib…but if someone sent me one of those things and I saw a timer telling me I couldn’t read the message anymore in like 30 seconds, the first thing I’m gonna do is open Notepad and do a good ole CTRL-A, CTRL-C and CTRL-V. (or Print Screen or “Save Page As” from your browser or the list goes on)
As far as trying to recover one…nope, sorry. I’d never heard of it before.
I don’t think you can retrieve the burned note once the timer expires since it’s done on the back end. Not sure if the note is actually deleted/purged from the system or just the link to the note is removed/expired