A more honest answer would be that I find I have around four to five hours of creative thinking in me each day. I try to organize my day around these bursts of insight so that I never write when my brain is fighting me. I find there is ample work to do in the remaining hours of the day doing the "drudgery" that comes with writing. There are ISBN numbers to purchase, SEO results to optimize, hand-written edits that must be typed, etc. I find that the key is separating out the creative from the mechanical.