Developing a time management plan takes experimentation because your needs and time demands are not the same as anyone else’s. In developing a time management plan, I experimented with suggested plans from a number of well-meaning people. You need to do the same. Try different methods, strategies, and plans. When you find a method, strategy, or plan that works for you—incorporate it into your life.
A note of caution: some/many of the methods, strategies, or plans you experiment with will probably need subtle changes to them to fully work for you. For example, a friend once told me to break my 12-hour day into two, four-hour periods and two, two-hour periods. He further suggested that I use the first four-hour portion of my day to study for tests and exams (I was in my first year of college then) and use the second four-hour portion of the day to do homework. The other two, two-hour periods I could use for other things. I tried this but found that four hours was too long for me to concentrate on one item. So, I adjusted the formula. I broke my 12-hour day into four, two-hour blocks and two, two-hour blocks. The first two-hour portion of the day was my morning routine. The next four, two-hour blocks were used to study different courses and to do homework for those courses. The final two-hour block was used as my evening routine, just before bed. This worked much better for me, and I used this formula for most of my educational career.
By the way, I recommend including a morning and evening routine. The morning routine makes sure you start the day in the right frame of mind, and the evening routine ensures you end the day well and signal your body that it is time to sleep. Another benefit of routines is it reduces the need to make decisions for those blocks of time.
Use advice from others as the starting point, and then make adjustments. You will find the one plan that works for you after a few trials. Once you find one, make whatever adjustments you need to, write it down (color code it if necessary), and post it where you do most of your work. It will become second nature after a few weeks, and you will see your productivity blossom.