The answer is D, because depending on what you do, you could sleep for hours for some days and not very much on others. Meaning, you won't ALWAYS wake up the same times, so it's not a very good and effective time management skill.
But if you let others know your schedule, they are more apt to not bother you. If you track the amount of free time you have, you will be able to plan for other activities better. And if you budget the amount of time you have for each activity, you will be able to know when you end and what you have time left for.