I'd say you should go based on hours or TODO entries per day.
That's why I suggest going by TODO-list entries. Those are concrete things that you know need to get done. You can even score them in terms of anticipated difficulty, then try to reach a certain number of points per day/week.
Think of yourself more as an editor than an author. An editor might spend a lot of time re-factoring, looking up syntax, trying to make things flow better, asking people for advice, etc. Amassing words and lines isn't your goal.