Structure is important, start working at at the same time. Try to have your break at fixed times. Schedule for off-screen times.
If you have structure in your day it is more easy to manage the number of working hours. You don't want to spend too less or too much time then you agreed.
If you do enjoy your work ( let's hope you do), try to stop at a fixed time, There is always a tomorrow. You need to relax and you will be suprised how some of your problems might be solved over night while sleeping.