I plan each and every day of work the night before. This means exactly what you think it does. I sit down each evening with my list of tasks that need completed, a Frictionless Planning Pad and a pen, and then I plan out the coming day, hour-by-hour, from start to finish. Now, you might think that this leaves me with very little flexibility, right? I'm bound to a schedule that has my entire workday mapped out. But I don't need flexibility in the normal sense. Flexibility, I'm sorry to say, inhibits productivity. Too many choices means you will make the wrong one. Or none at all.
Rarely is anything an emergency in our jobs. Most items can wait till the next day, and the rare few that can't are tasks that can at least be completed later in the day. The focus that I experience by limiting my schedule's flexibility enables me to get more done each day, and at a higher level of quality.
Planning builds focus and increases productivity. Don't be afraid of the boundaries it creates, because sometimes boundaries mean the difference between "done" and "done well".