Make an object appear in frame N and not frame 0 in SpriteBuilder

In SpriteBuilder, every object starts at frame 0.

I have some objects that will fall from the sky, but I want their falling animation (physics with gravity) to begin later in the scene, and not at 0.

Can I either have the objects exist at a certain frame? (i.e. insert empty frames before the object's first keyframe), or can I have the objects queue the physics gravity after a certain frame?

tia