I leave the mouse mesh shoved into my entrances
until the apple bloom, when one can be certain
of no clustering. I've not noticed any pollen
being knocked off foragers, and I use 1/2-inch
mesh.
Once the bees are not clustered, they can
drive off any voles or mice that want to
wander in, and by then, the incentive to set
up shop in a beehive (cold weather) is gone.