Cover the custard with plastic wrap and let cool slightly, then place in the refrigerator for at least 4 hours, until very cold. (mycookinggallery.blogspot.ru)
If your oven is not large enough to accommodate all the loaves at once, proof for about an hour and a half before placing them in the refrigerator until ready to bake. (wildyeastblog.com)
Then place in the refrigerator overnight (about 12 hours). (joyofbaking.com)