Help with cider project

so i currently have 4 gallons of cider in the carboy. i plan on splitting it 1.5 :2.5 or 2:2 gallon batches. reason of the split is half will be for my girlfriend. and the other half i plan on adding in oak cubes soaked in johnny walker double black. my thing is im not sure how much i should add to the cider. is there some rule of thumb or ratio of liquid to oak cubes?

The only rule of thumb I know of is, figure out how many cubes you think you should add, and then add much less. Maybe a quarter as much as you think you should. But it’s all a swag. Just go easy on it, or it could be Johnny and oak city, which believe it or not could actually make the cider difficult to drink for all but a real lover of overdoses of these things.

How long are you planning on leaving the cider on the oak?