To divide big Events into smaller groups, you can use the Raidgroups Feature.
Create new Raidgroups
Using Raidgroups in Calendarevent
When having more then one Raidgroup, you are now able to filter the Calendarevent for Raidgroups using the Raidgroup-Dropdown.
To assign characters to Raidgroups, use the Checkboxes in front of the Characters. A menu appears at the bottom of the page, offering a Dropdown for the Raidgroup.
After that, you can see at the Raidgroup Icon in which Raidgroup the Character is.