Well that was fun! I tried out the timeshift program and my PC duly went a bit mad. ntpq -p showed all being well.
Chromium threw a fit because news.ycombinator.com's SSL cert had expired and offered to reset the clock which it could not do, given that I'm not in the habit of running apps as root. My Kerberos tickets all expired so Evolution lost contact and so did quite a few other things. MariaDB dumped core. systemd's timers went berserk so things like my LetsEncrypt cert tried renew itself.
I'm still hunting through some odd looking log files but overall things seem to be back to normal when I reran timeshift and returned to current time.
Similarly with my Mac, within moments it became unusable. Even trying to reboot from the command line and I got a message that it was waiting to acquire a lock on /. Hard reset and everything is back to normal.
iOS devices had a bug that hard locks it if you set the time to 1/1/1970 (on US timezones, that sets it to negative territory), I can't believe they don't do any tests for their OSes to survive this...
Chromium threw a fit because news.ycombinator.com's SSL cert had expired and offered to reset the clock which it could not do, given that I'm not in the habit of running apps as root. My Kerberos tickets all expired so Evolution lost contact and so did quite a few other things. MariaDB dumped core. systemd's timers went berserk so things like my LetsEncrypt cert tried renew itself.
I'm still hunting through some odd looking log files but overall things seem to be back to normal when I reran timeshift and returned to current time.