For me it's 45-60 minutes, but longer pauses afterwards (15-30 minutes). I only started doing this recently, but so far with good results. The other thing that

For me it's 45-60 minutes, but longer pauses afterwards (15-30 minutes). I only started doing this recently, but so far with good results. The other thing that helps me since a long time is having a todo-list in which the top-task really always describes exactly what I'm working at now. Even if that task is only "figure out what to do next".