Is it too early in the season to start splitting & transplanting hostas?
Wayne County Michigan
Now is a great time to split and transplant hostas. They will have enough time to develop roots before winter. Be sure you water them well after transplanting and make sure the area continues to be moist as they develop roots. Apply a 6" layer of organic mulch, i.e. shredded leaves, around their base as this will decrease water evaporation and create a more even soil temperature, thus less stress on the hostas.
Here is an extension resource from MN that states that spring is the best time to transplant, but fall is also good as long as you make sure they get enough water. https://extension.umn.edu/flowers/hostas