As a graduate student I switch betwwen many things during each week. My activities consist of attending classes, doing homework, grading, working on my research and studying for exams. However I notice that from time to time I tend to procrastinate **and this happens mostly** when I have to switch from one task to another. or when I feel that a task is difficult and I am not yet sure of how to handle it. It also may occur when I work at home in Sundays.
It also happens when unexpected lab meetings interrupt me from my schedule.

My situation is not that I do not feel productive, but some hours per week can be lost due to this issue and I consider this to be important.

To protect me from distractions I have installed browser plug-ins that do not allow me viewing distracting websites more than 5 minutes per day.
I also try to keep track of how much time I spend on each task and have established a relatively stable weekly program.

However I believe I could benefit from better time management advices to handle procrastination...

What are your suggestions ?