Cooking times are approximate and do not include time to rehydrate dried ingredients or marinate. If you are not familiar with ingredients or preparation method, think of the time indicated as the minimum amount required. As you become accustomed to Japanese cooking, the techniques will become second nature and you will spend less time on dishes.
Difficulty is based on the number of key ingredients and main tasks (simmering, frying, etc.) involved, as below.
Very easy: up to 3 key ingredients; 1 main task
Easy: 5 key ingredients; 2 main tasks
Moderate: 10 key ingredients; 3 main tasks
Difficult: more than 11 key ingredients; 4 or more main tasks
For tasks, basic preparations such as washing and cutting ingredients, mixing seasonings and making dashi are not counted unless they are extensive or require multiple tools (separate pots and pans, for example).
Quite a few dishes are on the borderline, and even those labeled as difficult may not be very hard, depending on familiarity with ingredients and methods. Likewise, some dishes categorized as very easy may seem rather tricky if ingredients and tasks are new to you.