Forum:Valhalla during oppent turn

I'm not sure if I'm able to use Valhalla during my opponent turn, because it say's "once per turn, if i control no monster on the field I can special summon 1 fairy from my hand to the field" so does this mean I can special summon a monster during my opponent turn too? If so am I able to do it during my opponent battle phase too? example: like if all my monsters on the field are destroy, am i able to use Valhalla set a monster and save myself from a direct attack?