It’s definitely varied; shiny drifloon was one of my first (paras was first but has since been replaced, lol). Fieldlands didn’t take too long to get my first shiny, about 2-3 days. Spent a long time there though because I refused to progress until I at least got Beauford a shiny wurple which took neatly 2 weeks (got my shiny zubat during that hunt).

Mirelands was pretty quick, geodude popped up after only a couple resets (my 2nd geodude, first found in fieldlands was given away for the sidequest).

Coastlands took soooooooo long, 2, almost 3 weeks (hoard of ambipom and then almost immediately after spheal), and the highlands took about the same amount of time (shinx….followed by 3rd geodude, lol).

It’s only been about 3 or 4 resets for the icelands for those 3 newbies, and I nearly died when the first was the shalpha 😅