When you invite a new villager to move in and boot a current resident out, the one leaving will be in boxes immediately and the invitee will move in the very next day. And it'll be somewhat random where they will plop down their house. But it seems that you can actually influence it. I don't have it all down, so you should search for info if this is important to you. All I know is that they're less likely to place their house on designs and I think also flowers. I was lucky (?) and got Chai to place her house (resets, of course) in the exact spot I had cleared for her (flowers removed and designs placed around the 3x3 space I wanted).
Thanks. I didn't know the boxes thing happened immediately. My ears perked up when melsi mentioned them going in the exact spot, but I guess that's not guaranteed.
My only candidate is Flora and I feel bad about doing it. I would have to replace her with a peppy, and only Ketchup seems like a good candidate. But, I'll probably just leave it alone.