"Concurrent Event Groups" and "autoRefresh"

and how to Change the text "2 events"?

At this moment the group state is not persisted. This means it will reset to the original state on update().

You can customize the groups using onBeforeGroupRender:

dp.onBeforeGroupRender = function(args) {
  args.group.html = args.group.count + " events in this group";
};

See also http://api.daypilot.org/daypilot-scheduler-onbeforegrouprender/

OK cool thanks!

Saving the state would be perfect! ;)

Saving the state is difficult because the group doesn't have any id, it's an ad-hoc client-side group. Moreover, it's not guaranteed that the group will have the same members after .update() as the events are reloaded.

There is also a somewhat similar concept called "joint events" which lets you group events using an id and move them together:

http://java.daypilot.org/sandbox/Scheduler/EventsJoint.jsp

Theoretically, such a group could be collapsed but I'm afraid it's not exactly what you are looking for.