Your attention deserves a budget before your time gets one.
Two appointments can take the same hour and leave entirely different afternoons behind them. One ends when it ends. The other follows you into lunch, the next conversation, and the walk home. A calendar records duration more easily than residue.
When you plan, consider what an activity asks you to carry afterward. You may need a pause after a difficult conversation, or a quiet task after a demanding meeting. That is not wasted time between the real work. It is part of the cost of doing that work attentively.
What is taking more attention than its calendar slot admits?