When does an object reach its terminal velocity?

Terminal velocity is achieved, therefore, when the speed of a moving object is no longer increasing or decreasing; the object's acceleration (or deceleration) is zero.

As others have said, 8 seconds to get to 90% of terminal velocity. But if you're falling from outer space, you could reach speeds much higher than terminal velocity, and slow down when you reach the atmosphere. If coming in from a long distance, you'll burn up like a meteorite.

Explanation:

need to see circuit to get time constant