Make events' end date optional


I'd like to use the Events+ plugin for the site of a concert promoter. Right now you have to enter a end date and time in order to add a new event.In most cases it's not clear when a concert will end, so I don't want to force my client to enter date and time. Is there a way to make enterting the end date optional?
I now it doesn't have to be displayed in the front end template, but I don't like to tell my client, "just enter anything, no-one will see it anyways".

Also I'd like to add a "doors open"-time. Are the events-and-bookings.php and eab-admin.js as well as the template all the files that need to be modified?