I tend [sic] to get up, grab breakfast, sit in front of my computer [and not] get up until about an hour before dinner. I do this seven days a week, every week of the month, every month of the year.
That is from today’s Washington Post, Kids Section.
I have a different idea, taking effort as a scarce variable. Every day, stop writing just a short while before you really want to quit. The next day you will be very keen to get going again. For most mortals, your real enemy is the number of days when you get nothing written. Getting "not enough" done each day is a lesser problem.
Addendum: Here are my previous writing tips.