This all depends on how thick the slices of bread are. If the portions are too thick, they’ll take longer to soak up the batter. If the cuts are too thin, they’ll soak up the batter too quickly and won’t have a chance to cook properly. For denser bread, try soaking for 20 to 30 seconds, and for thinner or airy bread (like Challah or Brioche), try soaking them for less than 15 seconds. Just make sure to test a piece first before cooking the whole batch. This kind of bread can absorb the batter quickly and become soggy, so it’s best to start with less time and add more if needed. Some chefs recommend soaking time for about 5 minutes, but I find that to be too long. Too much soaking will result in soggy bread that falls apart when you cook it.