Guild Wars 2

This event is situated in Southsun Cove. Holding the four settlements (Point Pride, Kiel’s Outpost, Steampipe Steading, and Camp Karka) will cause the Crazed Karka Queen to appear.
You need to throw Karka eggs on the ground at her to break down her defenses. Players will have 10 minutes to defeat her. Defeating her will grant you a daily chest (account bound) containing two rares. There is also another chest you can loot that grant you 2 items. The Karka Queen have a cooldown timer so she won’t always spawn when all four settlements are under control. (Cooldown timer seems to be about 1 hr).

I have heard that the cooldown is about 1h and it have a 30 min spawn window.
But I cant say how accurate that is as I dont stay to farm southsun in between karka queens. However, it seems to be true as it appear to not spawn 1h after last kill even with 4/4 secure settlements.

I have seen it done consecutively 10min intervals before i think it is all luck of draw. longer time since it last died the better.