Staying focused during daily 9-5

I’m doing the Monday Hour One and Time Management Program and it has helped me to realize how much time I waste procrastinating before starting focus work. I’m good at my job and can produce high quality work that people are happy with in about 2-3 hours of focused work per day, but I’m in a job where you need to stay at your computer for the full eight hours of the work day. It seems like to my brain feels there is no incentive to be extra productive as it won’t result in me finishing early, and sees no benefit in working hard for the full eight hours as my boss is already happy with me. As a result I coast along for chunks of the day, getting distracted online etc. before focusing with one or two hours to go before the end of the day, and finally producing the desired work. When I reflect on the day, I don’t like how much time is wasted trying to get myself to focus. How can I break this cycle?