My sister got an enchilada recipe from a friend she wanted me to try. It said at the top "total time 45 min / 15 min active time". Fortunately, I read the recipe. The ingredient list assumed that your chicken was already poached and shredded - another 20 minutes - and that your tomatillo sauce was already made - another 20 minutes. Then the chicken had to be marinated - another 30 minutes. Only then do you get into the 45 minutes of assembly and cooking time stated in the recipe.
Why do recipe-writers do this? A time estimate isn't a vital part of a recipe, more of an added convenience for cooks. But it becomes extremely INconvenient when you time your meal according to the estimate and only then discover an extra hour of non-disclosed prep time.