I just brewed an Old Ale that's sitting in the fermentor.
I have a jar of Bourbon and Oak Cubes that has been waiting since July 4th.
The Cubes all have sunk, none are floating, though they all floated at the start.
I suggest this - depending on how long the cubes have been soaking in bourbon - pour in some of the liquid, and all the cubes, and taste a tiny sample. You taste it each week. If you think more bourbon taste is needed, pour in more.
Just be aware that the bourbon has absorbed a lot of the Oak flavor depending on how long its been sitting in a jar.
I am using 10 ounces of Bourbon and 2 ounces of medium toasted oak cubes. I almost think I have let this sit too long and it may be too oakish. So I will see how it is after adding half the bourbon. I tried adding a teaspoon to a stout and it was really good!
I had originally planned on brewing this in mid July, but the yeast I was sent was 3.75 months old so I needed a replacement and brewed a Kolsch instead.