As an object increases in altitude, its mass: decreases
or remains the same

No matter where you are, your mass stays the same. It's weight that changes. Also applies to any object.

Remains same

Explanation:

Mass of an object is measure of the matter it contains. It is independent of height. Commonly when we weigh something we measure its weight and not mass. Weight is a product of mass (m) and acceleration due to gravity (g).

As altitude changes, the amount of matter doesn't change thus the mass will remain constant. But due to the change in height the gravitational force will change and thus weight will vary.

First of all, the bolts wont hit the ground at equal time intervals because each bolt is constantly increasing. Therefore, the top will have different velocity with the bottom bolt at all times. this means that the bolts will speed up more as they are higher which will make the interval time shorter. therefore, the time will decrease