you have to edit the core files of fullCalendar to achieve this. in function renderSlotSegs
find the comment
// not enough room for title, put it in the time
and edit it according to your needs
to keep time and remove title you need to remove this:
eventElement.find('div.fc-event-time')
.text(formatDate(event.start, opt('timeFormat')) + ' - ' + event.title);
eventElement.find('div.fc-event-title').remove();
and replace with this:
eventElement.find('div.fc-event-title')
.text(formatDates(event.start, event.end, opt('timeFormat')));
eventElement.find('div.fc-event-time').remove();