I need to see the event time range in month view. Now I see only the start time. I read the documentation and didn't find a way to change this format.eventTimeFormat is not working because the end date is null.
Check the value you set for displayEventEnd https://fullcalendar.io/docs/displayEventEnd
This setting controls whether or not to display an event’s end time.
It is a Boolean with the defaults:
false // for dayGridMonth and dayGridWeek views
true // for timeGridWeek, timeGridDay, and dayGridDay