If you have two trays of ice cubes in the freezer, you can make an ice bath to cool the milk to fridge-cold temperature; this takes less than one hour. Then you add the cold cream and the rest of the (cold) milk and the ice cream mixture is ready for churning.
How to prepare an ice bath for fast chilling:
1. Pour the warm milk into a heatproof bowl made of glass or stainless steel; these conduct the heat well and help the milk to chill faster. Avoid using a plastic bowl; this will take forever to cool the milk.
2. Nest the bowl with the milk into a large empty bowl (large enough to fit the ice cubes on the sides) and fill the sides of the large bowl with ice cubes.
3. Taking care that no water slips into the bowl with the milk, pour as much cold water into the sides of the large bowl as needed so that the level of the water bath in the large bowl is 2 cm / 1 inch above the level of the milk in its bowl. How many ice cubes? Well, the more ice you put, the faster the milk will chill.
4. Refresh the ice bath with new ice cubes as they melt; if you have a thermometer, put ice cubes as needed to keep the temperature of the water bath below 10° C / 50° F. The lower the temperature of the water, the faster the milk will chill.
5. Stir often, leaving the spatula in the bowl during the cooling process. The milk is ready when it is fridge-cold (anywhere between 4-10° C / 39-50° F is perfectly ok)
6. Remove the bowl with the milk from the ice bath, and wipe the bottom with a kitchen towel
7. Finally add the rest of the cold milk and the cold heavy cream into the bowl with the milk and stir. The ice cream mixture is now ready for churning.