Instead of standard guitar tuning (from lowest string to highest, EADGBE), the song she is playing ("Chop Suey," by System of a Down) uses a non-standard tuning (CGCFAD). She is **referring to this non-standard tuning as , or "the devil's tuning."**
So when she says
>
it just means
> "It's time for [that song that uses] the devil ['s tuning]."
And when she says
>
she's simply announcing that she's going to retune her guitar to put it into this special tuning.
For what it's worth, in English the tuning she's using here is **not** commonly called "the devil's tuning," but "drop C tuning." When the term "the devil's tuning" is used in English (as here and here), it generally refers to a tuning that includes at least one tritone, the so-called "devil's interval."