Julie Morgenstern, time management expert offers this advice: Don’t over schedule yourself. You need to build in time cushions, and that’s going to vary depending on you and your business. Don’t schedule more than three hours’ worth of work in an eight- or nine-hour day, especially if you’re in a service-based business where clients call and you have to jump.
If you’re in an environment where someone asks for something and you have to respond, alternate hours: For every hour of scheduled activity, keep the next hour completely open, and then schedule an hour of planned and an hour of unplanned activities. That spreads you availability across the whole day and you still have enough private time to get uninterrupted work done.