Most authors I read write in small chunks of time (1hr~40min). I wonder if this is a writing technique. I always find myself writing for 3 to 4 hours straight (taking 5 minutes breaks). The thing is that when I start writing I want to put all my ideas into the paper (I mean screen) as fast as I can. I wonder if this is bad for writing. Is it a bad idea to write too many hours straight?
Different writers have different writing disciplines. Mark Twain said that his discipline was to write a certain number of pages per day, but he wrote in longhand and as he got older he began to write in a larger and larger hand, so that his actual output was less. He was, he confessed, a profoundly lazy man.
I read that Stephen King used the "pages per day" method as well, and this is not uncommon. The important thing in a longer work is the preparation — start by reading twenty or so pages back from the point you stopped the previous day. This lets you edit what you wrote as well as brings you back into the feel of the piece, so that when you get to that blank page you already have a full head of steam. Another nice thing about the "PPD" method is that it forces you to write something. If you write crap one day — and we all do — you can simply edit or delete it. But you will have at least gone through the exercise.
However long your daily session, another important consideration is not to write yourself out in a single day. Writing a longer work (which I assume is what you are talking about) is like running a marathon: you have to pace yourself. If you sprint too soon you will wear yourself out. Leave something for the next day, even if it is a juicy bit that fairly begs to be written. Especially if it is a juicy bit that begs to be written. That will give you something to look forward to. If you have ideas you are afraid you will forget, write them as notes and use them in the next day's writing.