No I didn’t. The days I mentioned were 2 real days, and I’ve never tried to change my system time because I was worried it’d mess up all the grottoes.
I still have about half my hidden grottoes left, but most of them I’ve lost because I’ve accidentally waited in the grotto for more than a day (as in I saved in the grotto and closed it for 1+ days), so the item/pkmn disappeared the next time I came on and never reset again.
This is also happened to a few people back in 2017 but I don’t think it was solved:
and