[Kevin Sevcik]

EDIT: Matt H. has a bad unit conversion up there. slip of a digit or some such. 0.41cfm * 12in/ft * 12in/ft * 12in/ft * 1min/60s = 11.8cis. By his reasoning, you'd get a ~7.5s lift. I think he's oversimplifying, but his simplification may still be more accurate than my complication below. If you test it, please do post the results here.

You can think of your air supply as 64*120 (in^3 * psi). Expanding to twice the volume means your air will have half the pressure. So when you extend, you're expanding to (64+76) in^3, so you'll be at:
64ci*120psi/140ci = ~54 psi.

So you have enough air to make the extension and stay near 60psi.

Now, when you go to retract, you dump all that nice air you just had. You're down to 64*54 storage. Retracting gets you to:
64ci*54psi/140ci = ~25 psi

So now we know what pressure you'll be down to when you're lifting. Finally, we can estimate how long it'll take to get back up to 60psi. Same rule applies for figuring out how many cubic inches we need to pump back in to get back up to 60 psi. It's a little less straight forward, though. We know we want to end with 140ci of 60psi, and we're starting with 25psi. So..
60psi*140ci = 25psi * X ci
X= 60psi*140ci/25psi = ~336ci

You're starting with 140ci, so you need to pump in about 200ci. And we have those nice flow rate figures for the pump. Now,to really figure this out well, I'd prefer an excel spreadsheet and a lot of math, but we can use those numbers to give you a good range. If we look at the flow rates at prssures near where you're starting and where you're ending, we can get a best case and worst case estimate on time. At 30psi, you have a flow rate of 0.62CFM, or about 18 ci/s. At 50 psi, it's about 12ci/s. So this gives you... (drumroll) A retract time between 11 s and 18 s. Figure on it being about 15 s.

So now that we know your original plan probably isn't going to work for you... Why are you using 60psi to extend your piston? I have no idea what your mechanism is, but I'm seriously doubting you need that much pressure to extend it. You can use two solenoids and set your extend pressure to something like 25-30 psi. That'd give you a retract time of about 5 seconds. Big difference, no?