Ball time usually depends on how you play the machine. Are you going for the "risky" (bottom playfield) shots or are you trying to his some upper playfield targets or ramps.
It also depends on the width of the outlane exits. There are some machines with no mercy there.
And if you try to play those fast, statistically you're about to drain relatively quickly.
Especially if the tilt plumb bob is high. Then you have even less chance to react on those returns.
It's interesting how all of you mentioned so many different machines. To answer the question myself, it's hard to say which one has the shortest ball time for me, but I can tell Fish Tales doesn't like me a lot