40 F and raining is perfect weather for an install. They will drift very little if at all.
I waited yesterday until it got up to 48 F and sunny. Tried shaking them out on a queen excluder so I could keep the drones out.
The weather was turning bad again, so I ended up not waiting for them all go down. They were gathering on the sides of the empty brood box that I was using above the excluder. After smoking them a bit, I just removed it all and shook them down on the frames (giving up on the drone idea).
I had a few in the air and I did end up with drift. All of my hives are close with 3 over wintered hives, all 6 had bees gathering on the front porch.
An hour later it got cold enough that if they had not made it inside they were unable to. I may have had a 100 or so that were still in the grass. I figure that was acceptable considering the 30,000 or so that were installed.