if i activate Dust Tornado during my opponents turn, and decide to set Mirror Force because of DT's last effect, can i activate that mirror force when they attack that same turn? or no because i cant play traps the same turn i set them?

Hope that answered your question.

No you cannot, traps have to be set for at least 1 turn, unless an effect allows it.

And due to the errata of Dust Tornado, you cannot even activate Quickplay Magic Cards if that's what you Set since they have the same rule as Traps (being that they have to be Set for at least 1 turn if you want to use them in your opponent's turn)

Basically, you're going to want to set cards that usually activate on your turn anyways like COTH....

Or just set another Dust Tornado or something like that to use later.

True, I save my Dust and MST for their own Heavy Storm/Dust/MST.

I've mainly used Dark Coffin and Statue of the Wicked or even, depending on the Deck, Kozaky's Self Destruct Button.