IT really comes down to taste. IMO you use the soaked chips and sample once per week until you get the desired taste you are looking for. If at the end of soaking on the chips you still desire more bourbon you can add it bottling time.
I brewed Denny's Bourbon Vanilla Porter and used the 350ml of bourbon a to a 6 gallon batch at bottling. After about 10 weeks bottle conditioning the beer is absolutely fantastic!
Nothing Left to do but smile and drink beer.....
The Commune Brewing Company-Perfecting the "art" of beer since 2010