On a general spirits level, I've not noticed really tangible oxidation in bottles I have owned for years. At least I found them enjoyable, even after several years of being open. Perhaps when in cask they were already slightly oxidised (these were cognac, spanish brandy, and scotch whisky). In regard to bourbon, I've never had a bottle open for more than a few months, but I doubt its much different.
The key is of course letting your tastebuds guide you. Don't down the bottle just because some folks recommend not letting it stay open for a period of time. Enjoy it, and if you note the spirit seems to start to go "downhill", then next time, you can enjoy it more quickly after opening.