Time to Feed has two targets: a creature an opponent controls and a creature you control. If only one of those creatures is a legal target when Time to Feed tries to resolve, the creatures won’t fight and neither will deal or be dealt damage. If the creature you don’t control is the illegal target, you won’t gain life when it dies.

If neither creature is a legal target when Time to Feed tries to resolve, the spell will be countered and none of its effects will happen.

If the first target creature dies that turn, you’ll gain 3 life no matter what caused the creature to die or who controls the creature at that time.