I hunt only groundhogs and coyotes now.
Yes, you’ll see more woodchucks feeding in the evenings and mornings, as they will stay in the cooler dens during extra-hot weather. Being creatures of habit, even the ones who normally have a feeding time in the morning, noontime, early afternoon, after/during rain, at dusk, etc. (ones I explain to my wife - as she rolls her eyes - as being “noon hogs”, “night hogs”, “rain hogs” when we see them feeding at their respective times) will all switch to cooler evening feeding in hot spells. Have also noticed over the years there is kind of an eating “dead” period from about mid-June through mid-August, before they really pig out for winter fattening.
If it’s more than a temporary decline in sightings due to weather, I’d put over-development/human encroachment as the number-one, more serious, reason; followed by coyote predation. Also, a few years back we experienced around here a large die-off from what I at least attribute to the possibility of a disease epidemic carried by some kind a flying vector that you would see around the entrance to every den entrance for a year; these weren’t blowflies, but some uncommon strain of biting insect.
But yes, sadly, there’s been a steady decline in most all wildlife in my area. Nothing now like it used to be 70+ years ago on my (Ohio) family farm. Too damned many people.