The summary you mention is showing the start and end times in one time zone (in San Francisco). Apple's Calendar app does not support multiple time zones in one event. However, in iOS and in the Mac version of Calendar your event will always display with the correct time for the zone in which your device is being used. The Mac version requires turning on Time Zone support.
Your flight is about six hours duration, but to display 8:15pm you would have to establish an event for this being the six hours travel time plus the difference in time between the two cities (which I gather is three hours). But if you create a nine hour event this will give you the wrong time when you arrive in Boston by a factor of three hours.
For your return journey you can create the event while you are in San Francisco and save yourself the burden of calculating the correct hours by using Boston as the chosen time. When you touch on the time (of departure) proceed then to touch on the Time Zone label which appears, then search for Boston. Enter the end time six hours later (arrival at your destination) also for Boston time. If you choose San Francisco the event duration would be nine hours. In other words, the start and end times must be set for the same location, but your phone will adjust this when you enter a different time zone.
I always the notes field to record the flight duration and number, plus local departure/arrival times in the 24 hour clock for clarity.
Alternatively you could create a nine hour event for your six hour journey, and be aware of the inaccuracy at your destination.
