Take samples (wine thief, bottom of auto siphon, Turkey baster). Rack away when you reach your desired level of flavor. Remember, the oak flavors are going to be a bit rough and sharp at this point, don't fret. The flavors will mellow.
I had 7.5 g/L medium toasted oak chips in the secondary of my recent oatmeal stout. after one week i pulled a sample and decided it was enough (on the edge of too much) so next time, i will take less and take more samples to optimize the timing a little...
I used 2oz medium toast chip before, left in for 2 weeks. Didn't get the flavor I wanted, I think I just didn't use enough chips though for a 5 gallon batch. Haven't used again, so this is my only frame of reference, sorry. Good luck!
