I use this work pattern when I'm doing particularly distasteful work, and it generally works well.

The only thing I'd advise is that if you're in a state of flow (in which the passage of time just disappears and your focus zeroes in completely), don't worry about maintaining a rigid time schedule.

Every so often, when I'm writing, I forget to check the clock and then it is 3 hours later and I realize that I've missed a meal. I wouldn't trade those times for very many things.