Truly effective teachers might spend a large chunk of time planning a large unit, the first time. However, following their reflection on the reception of the lesson and garnering student feedback, the next time will be much more fluid and purposeful, lessening the time but increasing the impact. Additionally, effective teachers do not always start from scratch; they collaborate with others to save time and share with others to improve practice.
Truly effective teachers are not hinged to any desk for a ridiculous number of hours every day. If you’re doing that, stop. If you find yourself grading papers endlessly, STOP. Talk to your mentor or talk to someone who just seems to “have it all together.” That person will have valuable information as to how to work not only effectively, but realistically.