All VTEC engines will not hit VTEC or the rev limiter untill the engine temp is up to normal operating temperature. It's monitored by the ECM. Besides the fact that it is not good to gun any cold engine, when a Honda engine switches to VTEC the oil pressure in the head is about 3 times what it is normally (think about a human's blood pressure when running hard on a hot day vs taking a nap on a cold day). For that to happen, the oil must be completely circulated throughout the engine and thin enough for a large amount to be pumped through very quickly.