First of all, you attach a script with

right?
Second of all
a timer would go like

right?

Finnaly how would i reset that and maybe make a cooldown sequence so you cant exploit the code to constantly use the code controlled by said timer?

You attached the script wrongly.

To attach you simply use ScriptPath = Mod.rte/Bla/TheFile.lua

Now, one thing with lua is that tabbing doesn't really matter.

And to reset timers you use TimerName:Reset();

Tabbing doesn't matter to the parser, but it does matter for readability. I'm way more likely to help somebody whose code is tabbed and readable (or, hey, you could even put in comments) than if their code is a big lump of characters.
Anyway, back on-topic:
Your Update function wouldn't do anything, currently - Timer:LeftTillSimMS() returns how long it'll be before a time is reached (in milliseconds). As well, you left out the "self." before the timer. As well, make sure that when you're calling a function, you use ":", not ".". This code would work, if you want the code to execute when 3 seconds has passed:

EDIT: ninja'd

ok I will try that