Depends on what you use. My personal favortie is Med Toast European (or Hungarian) oak beads (or cubes). Had great results. I would leave the oak in there for 6 to 8 weeks.
Do not bother try to save your oak for later use. They are cheap as chips and will not give the same flavors the second time around. I would not reuse oak beads any more than I would reuse a toungue depresser.