So for the first question, you can't invite another villager in until the first villager is plotted, otherwise the second will override the first. So it depends how quickly invited villager #1 plots.
For the second question TTing backwards any amount of time counts as one day forward. So say you invite villager #1 on a Monday, TT to Wednesday and find their plot, invite villager #2 in and TT to Friday to find the second plot. Now if you TT back to Monday, your game will act the same as if you had TTed to Saturday.
Hope that made sense