The cooldown for the boss is 4 hours and the duration of the access is 8 hours, that means you can do the following:
- 00:00 Get access to the teleport
- 00:30 Kill the boss for the 1st time
- 04:30 Kill the boss for the 2nd time
- 07:50 Enter the teleport before the 8 hours expire
- 08:30 Wait inside until the 4 hours cooldown for the boss is gone and kill it for the 3rd time (you won't be kicked from the cave when you reach 8 hours)
Obviously is very difficult to do this, since you need a lot of players, and always some players will have to leave etc... keeping a big enough team for all the 3x is really hard.
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Edit: I just realized you meant entering the Warzone area in general and not the bosses :| There is no cooldown to deliver points again and get another 8 hours of access.