Note that Chandler's approach very specifically did not involve getting a task done. He was talking about writing novels over the course of months or years, not little things he was putting off.

Also it's a task where inspiration is involved, so if he forced himself to write every day no matter what, some of it would be worthless because the ideas weren't there. The point of his approach is to make habits that ensure you accomplish something in the long run, regardless of whether you get something done today or not.