(self-evaluation is noisy)
Don't tell gwern ...
Although something like "hours worked in a productive manner" should be well quantifiable, for most professions.
Self-experimentation is causal inference with a sample size of 1 and selection bias, e.g. silly and doomed.
http://www.johndcook.com/blog/2013/02/04/four-hours-of-concentration/
And since this is the Internet, and facts are involved, our gwern turns up there also.