Does anyone know how long it takes for these to carbonate a 12 oz bottle?
It depends on the health and quantity of the yest remaining in the beer and the temperature where the bottles condition, as well as the strength and pH of the beer. There's no one answer, but if your beer is "normal", i.e. not excessively strong, not sour, and only recently pulled from the fermenter, 2 weeks would be a normal time if the bottles are at about 20c. After this time, just test them every now and again until you're happy.