Maria makes a large dish of curry on Monday, ready for her family to eat on Tuesday. She needs to put the dish of curry in the refrigerator but must let it cool to room temperature, 18°C, first. The temperature of the curry is 94°C when it has finished cooking.

At 6pm, Maria places the hot dish in a sink full of cold water and keeps the water at a constant temperature of 7°C by running the cold tap and stirring the dish from time to time. After 10 minutes, the temperature of the curry is 54°C.

It is given that the rate at which the curry cools down is proportional to the difference between the temperature of the curry and the temperature of the water in the sink.

At what time can Maria put her dish of curry in the refrigerator?