Attacks » Timeless GX
After time is called at the end of a match, what happens if I use Dialga GX's "Timeless GX" attack during the "plus three turns" part?
If you use Timeless GX when time is called during your turn, you would then get "Turn 1" instead of your opponent. Likewise, if you use it during Turn 1 you would also get Turn 2 and your opponent would get Turn 3, and so on... However, if you use it on the final turn of the match you do not get an extra turn.
Source: Ultra Prism FAQ (2018-01-19), TPCi Rules Team (2018-02-01)
Attacks » Timeless GX
When you use Dialga GX's "Timeless GX" attack does Poison still happen in between turns?
Nope, the attack says to "skip the between-turns step", so Asleep, Poisoned, Burned, and any other between turn effects also get skipped."
Source: Ultra Prism FAQ (2018-01-19), TPCi Rules Team (2018-02-01)