Plot resetting doesn't require time traveling at all. All you have to do is create a new character the next day after you have invited a dreamie in before you load an existing character, and keep creating new characters until you find a spot you want your villager to move in.
I don't know why the guide says to get dreamies before you landscape. You should actually do it in the opposite order if you are willing to plot reset. The whole point of plot resetting is to get villagers in places that you want them to go, so you should have a plan for where you want them to move in before you start trying to collect dreamies. If you don't want to plot reset and just leave it up to random chance, then yeah get your dreamies first because you'll have to build around their houses.
It also includes planting and cutting down trees and bushes, planting flowers, and setting up PWPs. Basically anything you do to alter the appearance of your town is considered landscaping.
Because the plot will appear on the 'new day', which is 6AM for Animal Crossing. If you haven't loaded an existing character on a day, then you're able to change where the plot moves on every new save file.
You can also load it on 5:59AM if you're not bothered waiting lol
Yeah. You can TT if you are really impatient to get started on plot resetting. I wouldn't recommend it though. When you acquire one of your dreamies, you should take some time to celebrate that because once you start plot resetting, you are going to start hating that villager very quickly when (s)he insists on trampling your paths and flowers.