Go to (in the top menu) iMovie/Preferences. Click on the Browser Button in the Preferences. Put a check mark in the top item. This will show the date range beneath your event name.
You can double click on the Event name in the Event Library and change the name.
There is no automatic naming that I know of.
Use the SHOW menu in the top bar for various options on displaying your events. You can show by year or by month within year for example. If your event has multiple days you can show days within the Event.