As per anabolic diet you should not carb load until 14 days of keto eating. This is to ensure the metabolic switch.
As to how long till your body starts using ketones for energy this is going to vary from person to person
As for ketostick, while they are helpfull they are not 100% accurate. For a ketostick to show ketones your body has to have an excess and then get rid of those ketones in your urine. You may very well be using ketones for energy and not have any extra to pee out so it can show negative but is positive