I started pumping at the six month mark and that seems to have also helped a bit in terms of increasing circulation and stretching. I had a decent growth spurt around 3 months. I can't say that pumping has added any length on a day to day basis, but it has made it easily noticeable when I'm "happy", which I like.
I haven't settled on meta or phallo yet, but I know the surgeon I've settled on wants guys pumping and using DHT cream for a certain number of months pre-op for metas. I'm probably close to two years out for surgery based on financials, but starting early on at least one of those things can't hurt.
Like someone mentioned above, the key to success with pumping is consistency. I think I read somewhere that someone recommended 2-3 times a day for a minimum of 15 minutes per session. I wake up, pump it up, detach the cylinder from the pump, and wear it around while I get ready for about 20 minutes. At the end of the day, I wear it for 20-30 minutes.