Heating times can vary depending on the size of the bottle you are using. As a general guideline, for a standard-sized 4 oz (118 ml) bottle, it is recommended to heat it for around 3 minutes using the Philips Avent SCF355 bottle warmer. For larger, 9 oz (266 ml) bottles, the heating time may need to be increased to approximately 4-5 minutes. Remember to always test the temperature of the contents before feeding to ensure it is not too hot.