Time Management – 2 tactical questions

This is a very tactical questions about how you manage your calendar and action item list.

Do you build in buffer time in your calendar for things that regularly run longer than expected–but not because of anything you can control? The most obvious example in my life is around travel. I usually add at least an extra hour to the expected travel time in my planning because flight delays are frequent. How do you plan for those types of delays that are possible/likely, but completely outside your circle of control? If you do use buffer time in your calendar, what do you do with the planned buffer time if it isn’t needed?