end is a property of an h-event that indicates the date and time of the end of the event. The value is always an ISO8601 timestamp with either day precision or second precision including timezone offset:
When an event includes an start date, the summary will be rendered in a human-friendly format with the least amount of duplicated information. For example, "November 5, 2015 from 6:00pm to 8:00pm (-0800)". This is handled by the date-formatter-php library.