Colder will mean a lower CO2 pressure. Not sure if it will speed it up though. I routinely carb brews at room temperature and it takes the same 3 weeks ( I always use the set it and forget it method....no shaking). One of the great things about having an extra CO2 bottle of two, when you put your beer in your keezer/keggerator it's already carbed and only needs to be chilled.