I have a couple of similar issues with the time settings when creating an event back-end (probably front-end too but not tried)
1. REQUIRES END DATETIME... I have this set to NO but if I don't enter anything in the end date field, it won't let me create the event telling me it's needed.
2. ALLOW TIME... I have this set to YES but this seems to make time MANDATORY.... if I try to create an event without a time it won't let me. Most of my events have a start time but undefined end time (and some all all day events).... So I want to do as this setting suggests, allow a time entry but not make it mandatory.