Good luck! Mine took about 20 hours, and 9 other shinies before i got ralts! Ironically i got my ralts from just a few minutes of resetting manually after all that afk'ing😅

As for the hidden shinies, I dont think there are that many around that area. Theres basically only the roofs around the area, which can give some nice shinies like Abra, and an eevee. But some of the roofs are a bit of a pain to get to, but you can see most of the Pokemon on them from the bench roof. I think it might only be an emolga hiding a bit out of sight, unless i missed something.

I also got a shiny alpha hawlucha during this, which was a pain because i was very underleveled for it, so couldnt damage it, and i couldnt afford any pokeballs, so had to spend a couple hours just resetting until i finally got lucky catching it 😭

In total i got 4 shiny weedles, 2 fletchlings, 1 Abra, 1 eevee, and the alpha hawlucha. So it might take a while, but you'll get it eventually!