Given the following about a spring:

mass = 20.0 kg
height initial = 5.25 m (above the ground)
height final = 2.17 m (above the ground with the mass attached)
delta y initial = 0.00 m

I have found the following:
Spring constant: 63.7N
It would take 576J to return the object to its original position.

How much power would it take to return the mass to its original position in 3.5s?