When using Smart Mode, Mellow knows how long your food can stay in the water bath before it is overcooked or unsafe to consume. Mellow does not cool the water once your food is ready, so it is important to remove your food based off of the instructions in the notification. Depending on what you are cooking, Mellow will send you instructions, like "your food is ready, please remove it within the hour."
If you are not able to remove the food packet when advised, unfortunately it may affect the desired doneness or may not be safe to eat.