No matter how long the slinky is, the bottom of the slinky will stay still (hover) until the top reaches it. Even if the slinky is over 1000 feet long.
OMFG NEW EXPERIMENTS
HOW IS GRAVITY EVEN REAL
OKAY LET ME EXPLAIN YOU A THING
Gravity acts on every part of an object, that much is true. However, what’s going on here is so much more complicated than gravity. The spring compresses because its shape means the rings want to be together. I’m sure we all know Newton’s Third Law: for every action there is an equal and opposite reaction - that is to say, for every bit of gravitational force bringing the top of the Slinky down, there is an equal amount of tension force bringing the bottom of the Slinky up. The bottom of the Slinky doesn’t move because the force of the rings bringing themselves up to meet the ring above them pulls it up at a rate equal to that of gravity.