(Photo : Reddit via r/TheSILPHRoad)
Everybody has the chance to catch Shiny Grimer in "Pokemon GO" and the good thing here is that it would be available almost anywhere, as long as users go out and drive around. However, if they cannot go out during this time of night, they can always use a location spoofer to venture and catch Shiny Grimer in the map.
What is more iconic in this spotlight hour is that "Shiny" Grimer has an increased chance of spawning in the wild and populated places as trainers go around and search for it. But not an increased chance of spawning the Pokemon itself.