Neither the calendar nor the event editor show me the time zone I'm in. I think at least the calendar ought to. The display of the time zone in the calendar may as well be an affordance (drop list) to adjust it without having to switch to the Profile Edit page and back (that's not saying to remove it from the Profile).

Adjusting the Start time does not cause the End time to adjust by the same amount. That's a common and handy feature.

The rich text formatting tools are absent a color picker.

Because events can generate reminders, and reminders go out as email, the group manager must be able to moderate the events (otherwise the option to allow subscribers to edit events is a means to bypass message moderation). Because the "Moderated" and "New Users Moderated" group settings are described with the generic "posts" it may be adequate to tie the moderation of events to those same controls (including the individual member's posting override, if any). A pending event should not be shown on the calendar to other members, and should not generate any reminders. Approval of the event would implicitly approve any reminders it generates.