To get an accurate picture of how much time you spend prepping for and/or commuting to meetings, add a custom field to your calendar items.
First, on the View tab, Current View group, click the Change View button. Then right-click any column heading and open the Field Chooser. Click the New button to create your new field. For example, name it Commute, with a Type of Number and a format of two decimal. Now, with your calendar in List view, you can add the number of hours or fractions of hours it takes you to get there.