I think this answer is relatively on target, from the book :Managing Time: Expert Solutions to Everyday Challenges (Pocket Mentor):
You cannot successfully manage your time if you don’t know how you should be spending it. The biggest problem new managers face is understanding their goals and priorities. They are not really sure what they should be doing.
Because of this uncertainty, new managers often spend time working on the wrong things or let others pull them into activities that aren’t directly tied to their priorities and goals. To better understand how you should be spending your time, work with your supervisor to clarify expectations and responsibilities.
At the same time, start to get a handle on how long your new responsibilities take so you can better estimate and plan your time as you grow in your new role.