A WORLD EVENT LEAVES WHEN THE EVENT DOES
How it is played
Faction
Armour type
Loot
Server
Timewalking is a week. World events are a fortnight. A seasonal campaign chapter closes with the patch. That makes this the one page on the site where ordering late genuinely costs you the thing rather than just delaying it, and the estimates say plainly whether a window will still be open when your order lands.
Flying unlocks for every character you have and every character you ever make in that expansion, which is why it is the best value row on this page and why almost nobody wants to do it twice.