If you're carbonating in a keg (since you mentioned psi), i have success with putting it at 30 then putting it in the fridge. After 24 hours, reduce to 12 or so. In 2 weeks it is ready.
That's great advice, thanks. I'm using a CO2 tank and regulator hooked up to an adapter to fit the 500ml green bottles. Tried one with my brother, hooked it up, turned the pressure to 30 and shook the bottle. It was too bubbly for me. I think I'll experiment with water to get the right amount of bubbly then try it with cider. I'm not sure if I'm going to try a keg yet. I'm only doing one gallon batches so far.