Answer:
It takes exactly the same time to rise as it does to fall,
This is proven by the equation of conservation of energy.
Kinetic Energy + Potential Energ = a constant
At the top the bullet has only potential energy (in the vertical direction)
At the bottom the bullet has only kinetic energy in the vertical direction.
If the given relationship did not hold, a perpetual motion machine could be constructed that extracted excess energy from the round trip.