The Instant Pot cooks food as it's coming to pressure. So when foods have a zero cook time, they cook as the pot is pressurizing. The time it takes for the pot to build pressure is the only time it takes to steam fresh broccoli! Remember, too, that food also continues to cook as you release pressure. Broccoli always needs a quick release so it does not overcook, which will happen if you allow the pressure to naturally release.