I attended a workshop last year that was called Finish on Time. There they talked about many tools that can help you during your Ph.D. studies to plan your time and handle stress.
A tool I still use is to plan my upcoming week in detail. Each Friday, I sit down and look at my calendar for what I need to do, then I think about what I want to do, and then I make my schedule. By doing this, I always know that I have time to do the things that I need to do, which helps me feel less stressed when there is a lot to do.
I write with a pencil what I plan to do, and I write what I did with an ink pen. Some weeks I follow my plan, but some weeks I have to change everything.
I know that this does not work for everyone, but it has helped me.