... here's the thing. No, Hang Time is not going to stop a fall, but gravity takes a perceptible, measureable amount of time to move an object - any object - a significant distance. A quarter-second for a half-meter; 1/3 a second for a full meter. (And yeah, it only goes faster after that.) The trick for the possessor of the two powers is to be using each at the right time.
You Wall Run, and just before you reach your limit of distance, you reach out to the wall ahead of you, put your hand there, and trigger Hang Time, which sticks you to the wall - and that's where you stop your Wall Run, because hey, you're using Hang Time to stop. Then, without moving the adhering limb(s), meaning maybe his hand and one knee; he gets ready to push off and Wall Run again; triggering Wall Run, he takes off a-running. Rinse; repeat.
Here's the thing - while on first read Hang Time requires you to be absolutely motionless, the specific thing(s) you cannot move are the points of contact that are providing the Hang Time. You could - I think - move any other limbs, so you could hang there with one hand and both knees (or just both knees!!) and draw a pistol and fire. Or - and I'm just spitballin', here - you could hang by one foot and the opposite hand, move the other foot/hand combo upwards, lock them into place, and 'free' the first pair - and thus ascend using only that. You'd move as using Unassisted Climbing, with a die bonus as per the power, but you would - could - still move. It's when you try to adjust the hand you're using to stick to the surface that you're heading down.
Or maybe I just want cool superninja shit in my game, I dunno.