Managing time is a difficult task. I never try to portray that this is an easy thing to undertake. This is something that will take time and will require some trial and error.
There is no perfect way of managing time that will work for everyone. Some people do better having a lot of structure, others prefer to not have any structure and work things out as they go. If either one of these ways work for you then keep doing that thing. Also keep in mind that people change. What may have worked for you back in college may not work very effectively now in your professional life.
I have found that a mix of structure and flexibility are that most effective for me. I like having a rough layout of what needs to happen and anytime sensitive appointments are part of the structure of the day. Everything else I let fall into the day as it fits I try to work small to large to gain momentum. And I log everything that I do. This way I can look back at the end of the day and see that I have accomplished quite a bit.
Again there is not magic bullet for time management. All the things that I share with you are merely things that have worked for me. They may or may not work for you. But it is better starting with something that has worked as opposed to starting with something that has never work for anyone. I recommend trying what I have done and keep what works and throw out what doesn't.
I hope this helps make you more effective and less stressed. To your success.