Another situation is when I set a time table; I always used time longer than I originally allocated.
I understand this as "I think I will need X minutes to complete task Y, but instead need e.g. double the time". I think here this is a matter of practice. Planning ahead and creating a realistic timetable will get easier each time IMO.
I start procrastinating, not by not doing it, but by doing slowly
I think you are already on the right track if you make a timetable. If you e.g. have to hand in a paper 4 weeks from now, then you could do a timetable on a week basis, like 1 week for research, 1 week drafting and 1 week finishing. Then add a "buffer time" of 1 week. Then break down the research into work units for that first week and so on.
I found the book "The Procrastinator's Digest" to be a short, but helpful primer of causes and strategies about procrastination. The ebook is available for a reasonable price.