Do not fill every minute of your day with appointments and tasks without buffers. There will always be new tasks coming up through out the day as well as interruptions or delays.
It is wise to plan 30% buffer throughout your day so that you have the time to react to such things without endangering your plan. In case you have spare time you can use it for conceptional work or to already complete tasks due later.
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Great post. I will read your posts frequently. Added you to the RSS reader.