If you invite them from another town, it'll be the next day; if you invite them from the campsite, it'll be two days later. Although these move-ins can be delayed if (I think) there's an event or another villager moving in/out.So, I was thinking of trying out that little trick which allows you to decide where a villager moves in your town, and, although I have no reason to try it now, it would come in handy for when there's a villager moving and I'm going nuts over whether or not the new villager will mess up a part of my town. So, I understand most of what I've heard about performing the trick, but, I've heard that you have to do it on the day you know the new villager will be moving in, and, I don't know how I'm supposed to know when that will be. So, how do I know?
If you're down to eight villagers and are waiting for a random move-in, you have a chance of getting one each day you're at eight (with the chances increasing as each day passes). So you should just check in with a new character every day, and remember to save the character even if you don't see a plot, otherwise one could still show up once you load up your mayor.