You need more than two announcements.
Players are busy, just loging in, not paying attention, etc, etc.
Looks like 68Hawk was announcing like before the CM's had the "everybody" channel.
One announcement at 30, 15, 10, and 5min is more than reasonable, so 4 as opposed to 2.
With only two you will have many players miss 'em and not fly the Special Event that they might have had they caught it.
(my worthless 2 cents)