MTG. Do instant cards that bring toughness to 0 kill creatures?

A creature whose toughness is 0 dies when state based effects are check. SBEs are checked whenever someone would gain priority to do something so a creature which becomes a 0/0 then back up to a 3/3 (for instance) during the resolution of an ability or spell would not die because SBEs would not have been checked yet. Something that says "until end of turn" means that when the end of turn step comes around, the effect drops off. A 0/0 creature does not come back from the graveyard at the end of turn.