Once you have put water in, sealed the pot and selected the cooker setting, the pot will start to heat up. As the water starts to boil, the pressure will start building inside. The food will only cook under pressure. The thing with instant pots is that they are built to heat up evenly from all sides. For frozen food to thaw and start cooking, it will take about 25 to 30 minutes for the pot to heat up. For other types of foods, it will take about 10 to 15 minutes for the pot to heat up evenly.