Paul Graham wrote a popular essay a year ago contrasting the "Maker's Schedule" with the "Manager's Schedule":
The manager's schedule is for bosses. It's embodied in the traditional appointment book, with each day cut into one hour intervals. You can block off several hours for a single task if you need to, but by default you change what you're doing every hour.
When you use time that way, it's merely a practical problem to meet with someone. Find an open slot in your schedule, book them, and you're done.
Most powerful people are on the manager's schedule. It's the schedule of command. But there's another way of using time that's common among people who make things, like programmers and writers. They generally prefer to use time in units of half a day at least. You can't write or program well in units of an hour. That's barely enough time to get started.
Marc Andreesen wrote a post a couple years before Graham recommending a something similar: as much as possible don't keep a schedule, don't agree in advance to meetings that can interrupt the most important to-do of the current moment.
It's true that for some creative pursuits you need long, uninterrupted stretches of time to get work done. I try to batch my calls / meetings for just this reason. But one twist: if you have literally nothing on your calendar for a day — and for enthusiasts of the Maker's Schedule, this is the goal — procrastination becomes easier, in my experience.
When I have nothing on today's calendar it's easy to dick around during any one of my morning routine stages: wake up, breakfast, email, workout, shower, lunch. If I don't have any anchor external commitment, I can say to myself, "If I start real work at 2 or 3 PM, what does it matter?"
By contrast, if I have a call scheduled at 1:30 PM (my usual time for doing calls), I keep focused on swiftly moving through my morning routine in time to do the call. Otherwise, my whole day is thrown off. Then, when the call's finished, I'm ready to immediately dive into real work for the rest of the afternoon / night. (I'm up until 1:30 AM.)
Bottom Line: The idea of a day totally free of any external commitments or obligations sounds good in theory yet increases the likelihood I procrastinate. On the other hand, a day full of meetings or obligations means I get nothing done. The optimal point is one or two obligations which mark the passing of the day and create a sense of urgency about how I spend the time that's all mine.