Probably not hibernating in your eaves. Bats usually go to deep-ish caves, mine tunnels or the like for the winter, where the temperatures will be constantly cool, unlike the eaves which will fluctuate between VERY cold to warm on a sunny day. I might wait another week, just to be sure no confused youngsters are around, and then seal things up. Bats can get through pretty small spaces, so double check even the most unlikely places.

Dibbit is right, most of our MI ones migrate to the caves north of us. They are kept rather secret in location, since the bats are pretty helpless in hibernation and no one wants them damaged.

There are ALWAYS some who don't get the message, try to winter over in other places. We usually get 1-2 that just appear in the house during winter. We have never figured how they get in! We catch them and put them outside. They probably die, but I can't house them till spring.

I would go ahead with my house fixing, plug up all openings. Bats are very flexible, can fit thru holes less than the size and thickness of a dime. Will help keep out those Asian Ladybugs too. A friend got them in the wall, had to have the whole wall rebuilt because of the excrement and dead bodies damaging the walls and wood of structure! Nest area was HUGE and particles in air were making her sick.

Ugh, yeah we have bats in our belfry too..or more like they are living in the tiny spaces in our vinyl siding! Once every few years or so a poor little myotis gets stuck and can't get out..and we find a crunchy dried up body sticking out of the siding way up high. :( There isn't much space at all, we have the siding nailed flush with the insulation, and then that's nailed onto the plywood of the outside of the house. They don't have many places to go, but we did get one that got into the eaves, and flew into the house, luckily he went out the open door!

This is a good site that will give you plenty of info: www.oit.itd.umich.edu/projects/ADW.
I have had bats in an old house and they stayed all winter. There are 9 different species of bats in Michigan. There is one kind that winters over in trees, while most migrate south to caves and the like. Some even travel to Mexico, I think it is the free tailed bat. Any way you should identify what specie that you have (there could be several different species roosting together) before repairs. See if they stay or go then proceed from there. If they stay I suggest holding off until spring when they are active, then when they leave for the night block their entry ways. Best for all. Hope this helps.