A message will appear in the in-game chat and the middle of the screen listing the active battlegrounds at the relevant starting times (and when they are deactivated again).
Starting Tuesday, 26th April 2016, the battlegrounds listed above will become available around the clock again, together with their regular rewards.
** Before and after the event, players must register for this battleground in a full 20-player pre-made to play against another group of 20 players. Although the text will remain the same, during the event you'll be able to register for this alone or as a pair (like the regular Corsairs' Stronghold).