We hiked Grinnell last October from the Fish Creek Trailhead. It is a flat mountain, so finding the summit marker is difficult. The road to Fish Creek is recommended for high clearance vehicles only.
Once you get there, you pretty much have the trail to yourself. We saw a few hunters (it was October) and maybe a couple of hikers as well. Beautiful hike up.
Not sure where the snow level is right now on that side of the mountain. There was snow out of South Fork at about 9,000 elevation on 5/3/20.