Imagine this scenario: You get up early on your day off to write. You've prepared perfectly: last night you went to bed early, right after putting together a clear, itemized list of writing goals you'd like to achieve by noon the next day.
Saturday morning rolls around, your alarm goes off, and instead of snoozing for another hour, you get right out of bed. You go directly to your computer and start writing--without checking email or doing any undirected internet surfing first. Soon, you're in a deeply focused flow state, typing away.
A few hours later, you look up. You've finished every single one of your goals, and it's only 9:00am!
What do you do next?
As I see it, you have two choices:
1) Quit. Give yourself a break. Knock off for the day and feel proud that you accomplished so much so quickly.
2) Keep going. You're in a highly productive state, and so you must take full advantage. You could have an outlier day of massive writing output.
Let me congratulate you on setting clear goals and getting up early to tackle them. That alone sets you apart from the dilettantes. But if you need help choosing between these two options, you clearly need to rethink your priorities as a writer.