Okay, I will post the problem here, so everyone knows it.
I realize that I really need to update the demo. I will do that soon, because some things aren't clear enough, and I'm sorry for that, I couldn't think of a more elegant way to do that.
So, about the Time LIMIT command, a bad use will make the game slow as hell, because it would create a lot a limits that needs to be checked every frame. For example, with the demo that Daisetsu sent me (thanks a lot to him for that), in 11 seconds it would create 7236 limits. You can imagine that after a few seconds, the lags would make the game unplayable.
I just want to say that it's not Daisetsu's fault. His way of thinking wasn't bad, it just doesn't fit the way I created the plugin.
So, let's go step by step.
Set the time limit

Here's the mistake. There's a time limit set from 8am to 6pm that will turn the switch A on, it's ok. There's no actual problem with that. The problem comes after. There is nothing, and that's the problem. And as the event is set to parallel, it will, in parallel to the game, ask my plugin to create a new Time LIMIT from 8am to 6pm a lot. I don't know exactly how many times a second, but it should be near 60 times a second, I guess, as the game runs at 60fps when it's smooth.
So, to solve the problem, you should just turn on the switch B, like that :

Page 1 is correctly set, now.
Page 2
For the second page, here's Daisetsu's page: (I just changed the contents)

As you can see, page two is what happens when the switch A is turned on (so between 8am and 6pm). This should be the 3rd page. As you should know, RPG Maker will take the page on the very right first, and if it can't, it goes left, and left, and left, and so on until page 1. So, as this page won't always be available but the switch B will always be on, you should make the page 2 as what happens when the switch A isn't on and the page 3 as what happens when the switch A is off. An example is better than words, so here's what I mean:

As you can see here, the switch B is the condition to reach this page. That means that page 1 will be executed one time as a parallel event, then it will switch to page 2, so it creates
only one switch.

And here, you can see that switch A is the condition to reach this page (I chose switch A here because the plugin command says that it will turn on and off switch A). So between 8am and 6pm, it will change the event to a woman that shows us her back, with an action button that makes her speak to us and show the text. Nothing really hard, but it explains pretty well how the plugin command works.
I hope it's clearer now, and I wish you a great game making and I hope it will solve some performance issues you're having !
EDIT : V 1.3.4 out!
* Solved a bug where Light LIMIT would turn on lights again after a battle, even if they aren't supposed to be turned on.