The Time in zones tab displays a visual summary of your time in zones for the completed activity. For activities containing multiple types of zones, you can toggle between items, such as heart rate, power, and pace to see your time in zone based on on your preferred primary metric.  Below the graph, your time in each zone is also displayed as a percentage and total time. 

This data can also be added to your single page activity view by adding a new widget for Analysis > Time in zones