These docs are for an old release.
Info on upgrading to v6
eventDurationEditable
Allow events’ durations to be editable through resizing.
Boolean, default: true
You must enable the interaction plugin before using this setting.
See code samples on the editable article
This option can be overridden on a per-source basis with the durationEditable Event Source Object option or on a per-event basis with the durationEditable Event Object option.