You know how there are different speeds? Well, I want to know if there is any way to detect them. Then, if so, what are the different rates a count down timer goes down?

Deaths go at about 8 times a second on normal speed when you have hypertriggers, from there it's quite easy to figure out. And no, you can't detect the game speed, since the trigger speed also changes with the game speed.

But I remember a tutorial before SEN died the first time... it involved a unit being order or something like that.

Yes you can detect game speed, theres a test map on Maplantis by Kenoli that detects every speed, just wait til' it's back up.

Not so fast, my young padawan.
Waits always wait the same time (real-time) on any speed.
So you can make a 10s (or w/e) wait and set a switch after.
And as long as the switch is cleared you let a dc run. Depending on the value of the dc you can determine the current game speed.

Do waits really? Then how come hypertriggers run at different speeds for different game speeds?

Yes, they do.

As you know sc doesn't wait exactly 0ms - which wouldn't be possible anyways - it waits 84ms.

Hyper triggers force the sc engine to check the triggers as fast as possible.
Which is every game tick. And this game tick depends on the playing speed.

Again, if you don't believe me, I can attach a test map. I wouldn't claim such things if I weren't sure.